参考：https://blog.csdn.net/wudinaniya/article/details/81094578
1、首先去mysql官网下载rpm包，一个是server包一个是client包。官网下载地址：https://www.mysql.com/downloads/
这里用mysql community server里边的。这里使用的是5.7.x版本了，不使用Mysql8.x版本了。
我这里使用的是Centos7.x版本的64位操作系统，使用mysql5.7版本的数据库。查看linux操作系统版本和系统内核版本，如下所示：
1 [root@k8s-node3 ~]# cat /etc/redhat-release # 查看操作系统版本 2 CentOS Linux release 7.6.1810 (Core) 3 [root@k8s-node3 ~]# uname -r # 检查系统内核版本 4 3.10.0-957.el7.x86_64 5 [root@k8s-node3 ~]#
选择对应的Linux版本和x86/x64进行下载，可以选择 RPM Bundle，下载完记得解压 tar -xvf xxx.tar。
可以离线下载上传或者在线下载包，如下所示：
1 [root@k8s-node3 package]# wget https://downloads.mysql.com/archives/get/p/23/file/mysql-5.7.30-1.el7.x86_64.rpm-bundle.tar 2 --2020-07-15 13:46:49-- https://downloads.mysql.com/archives/get/p/23/file/mysql-5.7.30-1.el7.x86_64.rpm-bundle.tar 3 Resolving downloads.mysql.com (downloads.mysql.com)... 137.254.60.14 4 Connecting to downloads.mysql.com (downloads.mysql.com)|137.254.60.14|:443... failed: Connection refused. 5 [root@k8s-node3 package]# wget https://dev.mysql.com/get/Downloads/MySQL-5.7/mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar 6 --2020-07-15 13:47:14-- https://dev.mysql.com/get/Downloads/MySQL-5.7/mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar 7 Resolving dev.mysql.com (dev.mysql.com)... 137.254.60.11 8 Connecting to dev.mysql.com (dev.mysql.com)|137.254.60.11|:443... connected. 9 HTTP request sent, awaiting response... 302 Found 10 Location: https://cdn.mysql.com//archives/mysql-5.7/mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar [following] 11 --2020-07-15 13:47:16-- https://cdn.mysql.com//archives/mysql-5.7/mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar 12 Resolving cdn.mysql.com (cdn.mysql.com)... 104.85.161.42 13 Connecting to cdn.mysql.com (cdn.mysql.com)|104.85.161.42|:443... connected. 14 HTTP request sent, awaiting response... 200 OK 15 Length: 598026240 (570M) [application/x-tar] 16 Saving to: ‘mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar’ 17 18 20% [=================> ] 125,263,632 2.17MB/s eta 4m 55s
也可以细化下载，下载须要的mysql组件，有4个：分别是 server、client、common、libs。
卸载旧版本的MySql，如果没有的话，则跳过即可，直接安装mysql。
1 [root@k8s-node3 package]# rpm -qa | grep mysql 2 [root@k8s-node3 package]#
如果有的话，将会列出旧版本MySql的组件列表，逐个删除掉旧的组件，使用命令rpm -e --nodeps {-file-name}进行移除操作，移除的时候可能会有依赖，要注意一定的顺序，{-file-name}是待删除的mysql的文件。我这里是没有，直接略过了。
2、使用 rpm 命令方式安装mysql组件，使用命令rpm -ivh {-file-name}进行安装操作。按照依赖关系依次安装rpm包 依赖关系依次common→libs→client→server。如下所示：
备注：在ivh中， i-install安装、v-verbose进度条、h-hash哈希校验。
1 [root@k8s-node3 package]# rpm -ivh mysql-community-common-5.7.30-1.el7.x86_64.rpm 2 warning: mysql-community-common-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 3 Preparing... ################################# [100%] 4 file /usr/share/mysql/czech/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 5 file /usr/share/mysql/danish/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 6 file /usr/share/mysql/dutch/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 7 file /usr/share/mysql/english/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 8 file /usr/share/mysql/estonian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 9 file /usr/share/mysql/french/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 10 file /usr/share/mysql/german/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 11 file /usr/share/mysql/greek/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 12 file /usr/share/mysql/hungarian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 13 file /usr/share/mysql/italian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 14 file /usr/share/mysql/japanese/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 15 file /usr/share/mysql/korean/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 16 file /usr/share/mysql/norwegian-ny/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 17 file /usr/share/mysql/norwegian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 18 file /usr/share/mysql/polish/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 19 file /usr/share/mysql/portuguese/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 20 file /usr/share/mysql/romanian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 21 file /usr/share/mysql/russian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 22 file /usr/share/mysql/serbian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 23 file /usr/share/mysql/slovak/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 24 file /usr/share/mysql/spanish/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 25 file /usr/share/mysql/swedish/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 26 file /usr/share/mysql/ukrainian/errmsg.sys from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 27 file /usr/share/mysql/charsets/Index.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 28 file /usr/share/mysql/charsets/armscii8.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 29 file /usr/share/mysql/charsets/ascii.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 30 file /usr/share/mysql/charsets/cp1250.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 31 file /usr/share/mysql/charsets/cp1251.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 32 file /usr/share/mysql/charsets/cp1256.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 33 file /usr/share/mysql/charsets/cp1257.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 34 file /usr/share/mysql/charsets/cp850.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 35 file /usr/share/mysql/charsets/cp852.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 36 file /usr/share/mysql/charsets/cp866.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 37 file /usr/share/mysql/charsets/dec8.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 38 file /usr/share/mysql/charsets/geostd8.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 39 file /usr/share/mysql/charsets/greek.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 40 file /usr/share/mysql/charsets/hebrew.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 41 file /usr/share/mysql/charsets/hp8.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 42 file /usr/share/mysql/charsets/keybcs2.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 43 file /usr/share/mysql/charsets/koi8r.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 44 file /usr/share/mysql/charsets/koi8u.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 45 file /usr/share/mysql/charsets/latin1.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 46 file /usr/share/mysql/charsets/latin2.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 47 file /usr/share/mysql/charsets/latin5.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 48 file /usr/share/mysql/charsets/latin7.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 49 file /usr/share/mysql/charsets/macce.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 50 file /usr/share/mysql/charsets/macroman.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 51 file /usr/share/mysql/charsets/swe7.xml from install of mysql-community-common-5.7.30-1.el7.x86_64 conflicts with file from package mariadb-libs-1:5.5.60-1.el7_5.x86_64 52 [root@k8s-node3 package]# rpm -ivh mysql-community-libs-5.7.30-1.el7.x86_64.rpm 53 warning: mysql-community-libs-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 54 error: Failed dependencies: 55 mysql-community-common(x86-64) >= 5.7.9 is needed by mysql-community-libs-5.7.30-1.el7.x86_64 56 mariadb-libs is obsoleted by mysql-community-libs-5.7.30-1.el7.x86_64 57 [root@k8s-node3 package]# rpm -ivh mysql-community-server-5.7.30-1.el7.x86_64.rpm 58 warning: mysql-community-server-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 59 error: Failed dependencies: 60 mysql-community-client(x86-64) >= 5.7.9 is needed by mysql-community-server-5.7.30-1.el7.x86_64 61 mysql-community-common(x86-64) = 5.7.30-1.el7 is needed by mysql-community-server-5.7.30-1.el7.x86_64 62 [root@k8s-node3 package]# rpm -ivh mysql-community-client-5.7.30-1.el7.x86_64.rpm 63 warning: mysql-community-client-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 64 error: Failed dependencies: 65 mysql-community-libs(x86-64) >= 5.7.9 is needed by mysql-community-client-5.7.30-1.el7.x86_64 66 [root@k8s-node3 package]#
在安装 mysql-community-libs-5.7.30-1.el7.x86_64.rpm 时有可能会报错，这个是mysql依赖错误，解决方法是：清除yum里所有mysql依赖包。
1 [root@k8s-node3 package]# rpm -qa|grep mysql 2 [root@k8s-node3 package]# yum remove mysql-libs 3 Loaded plugins: fastestmirror, langpacks, product-id, search-disabled-repos, subscription-manager 4 5 This system is not registered with an entitlement server. You can use subscription-manager to register. 6 7 Resolving Dependencies 8 --> Running transaction check 9 ---> Package mariadb-libs.x86_64 1:5.5.60-1.el7_5 will be erased 10 --> Processing Dependency: libmysqlclient.so.18()(64bit) for package: 2:postfix-2.10.1-7.el7.x86_64 11 --> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: 2:postfix-2.10.1-7.el7.x86_64 12 --> Running transaction check 13 ---> Package postfix.x86_64 2:2.10.1-7.el7 will be erased 14 --> Processing Dependency: /usr/sbin/sendmail for package: redhat-lsb-core-4.1-27.el7.centos.1.x86_64 15 --> Restarting Dependency Resolution with new changes. 16 --> Running transaction check 17 ---> Package redhat-lsb-core.x86_64 0:4.1-27.el7.centos.1 will be erased 18 --> Finished Dependency Resolution 19 base/7/x86_64 | 3.6 kB 00:00:00 20 centos-gluster7/7/x86_64 | 3.0 kB 00:00:00 21 extras/7/x86_64 | 2.9 kB 00:00:00 22 extras/7/x86_64/primary_db | 205 kB 00:00:00 23 updates/7/x86_64 | 2.9 kB 00:00:00 24 updates/7/x86_64/primary_db | 3.0 MB 00:00:00 25 26 Dependencies Resolved 27 28 ================================================================================================================================ 29 Package Arch Version Repository Size 30 ================================================================================================================================ 31 Removing: 32 mariadb-libs x86_64 1:5.5.60-1.el7_5 @anaconda 4.4 M 33 Removing for dependencies: 34 postfix x86_64 2:2.10.1-7.el7 @anaconda 12 M 35 redhat-lsb-core x86_64 4.1-27.el7.centos.1 @base 45 k 36 37 Transaction Summary 38 ================================================================================================================================ 39 Remove 1 Package (+2 Dependent packages) 40 41 Installed size: 17 M 42 Is this ok [y/N]: y 43 Downloading packages: 44 Running transaction check 45 Running transaction test 46 Transaction test succeeded 47 Running transaction 48 Erasing : redhat-lsb-core-4.1-27.el7.centos.1.x86_64 1/3 49 Erasing : 2:postfix-2.10.1-7.el7.x86_64 2/3 50 Erasing : 1:mariadb-libs-5.5.60-1.el7_5.x86_64 3/3 51 Verifying : redhat-lsb-core-4.1-27.el7.centos.1.x86_64 1/3 52 Verifying : 2:postfix-2.10.1-7.el7.x86_64 2/3 53 Verifying : 1:mariadb-libs-5.5.60-1.el7_5.x86_64 3/3 54 55 Removed: 56 mariadb-libs.x86_64 1:5.5.60-1.el7_5 57 58 Dependency Removed: 59 postfix.x86_64 2:2.10.1-7.el7 redhat-lsb-core.x86_64 0:4.1-27.el7.centos.1 60 61 Complete! 62 [root@k8s-node3 package]#
注意：有的系统可能不太一样，没有mysql-libs,而是mariadb-libs,此时要移除的则是mariadb-libs。
1 [root@k8s-node3 package]# rpm -qa|grep mariadb 2 [root@k8s-node3 package]# yum remove mariadb-libs
清除完yum里所有mysql的依赖包后，再次安装mysql组件就不会报错了，如下所示：
1 [root@k8s-node3 package]# rpm -ivh mysql-community-common-5.7.30-1.el7.x86_64.rpm 2 warning: mysql-community-common-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 3 Preparing... ################################# [100%] 4 Updating / installing... 5 1:mysql-community-common-5.7.30-1.e################################# [100%] 6 [root@k8s-node3 package]# rpm -ivh mysql-community-libs-5.7.30-1.el7.x86_64.rpm 7 warning: mysql-community-libs-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 8 Preparing... ################################# [100%] 9 Updating / installing... 10 1:mysql-community-libs-5.7.30-1.el7################################# [100%] 11 [root@k8s-node3 package]# rpm -ivh mysql-community-server-5.7.30-1.el7.x86_64.rpm 12 warning: mysql-community-server-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 13 error: Failed dependencies: 14 mysql-community-client(x86-64) >= 5.7.9 is needed by mysql-community-server-5.7.30-1.el7.x86_64 15 [root@k8s-node3 package]# rpm -ivh mysql-community-client-5.7.30-1.el7.x86_64.rpm 16 warning: mysql-community-client-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 17 Preparing... ################################# [100%] 18 Updating / installing... 19 1:mysql-community-client-5.7.30-1.e################################# [100%] 20 [root@k8s-node3 package]#
我这里server安装失败了，我这里强制安装，先安装一下，如下所示：
1 [root@k8s-node3 package]# ls 2 mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar mysql-community-libs-5.7.30-1.el7.x86_64.rpm 3 mysql-community-client-5.7.30-1.el7.x86_64.rpm mysql-community-server-5.7.30-1.el7.x86_64.rpm 4 mysql-community-common-5.7.30-1.el7.x86_64.rpm 5 [root@k8s-node3 package]# rpm -ivh mysql-community-server-5.7.30-1.el7.x86_64.rpm --nodeps --force 6 warning: mysql-community-server-5.7.30-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY 7 Preparing... ################################# [100%] 8 Updating / installing... 9 1:mysql-community-server-5.7.30-1.e################################# [100%] 10 [root@k8s-node3 package]#
注意：执行 yum remove mysql-libs命令后，会自动删除掉 /etc/ 下的 my.cnf 文件，对于安装mysql组件，只有安装了 mysql-community-server-5.7.30-1.el7.x86_64.rpm 组件，才会在 /etc/下生成 my.cnf 文件 和 my.cnf.d 文件夹。
1 [root@k8s-node3 package]# ls /etc/my.cnf 2 /etc/my.cnf 3 [root@k8s-node3 package]# ls /etc/my.cnf.d/ 4 [root@k8s-node3 package]# ls /etc/my* 5 /etc/my.cnf 6 7 /etc/my.cnf.d: 8 [root@k8s-node3 package]#
在/var/lib/下可以看到以下三个文件夹mysql、mysql-files、mysql-keyring，如下所示：
1 [root@k8s-node3 package]# cd /var/lib/ 2 [root@k8s-node3 lib]# ls 3 AccountsService color flatpak glusterd lldpad mysql-keyring polkit-1 rpm-state tpm yum 4 alsa colord fprint gssproxy logrotate net-snmp postfix rsyslog tuned 5 alternatives containers fwupd hyperv machines NetworkManager pulse samba udisks2 6 authconfig dbus fwupdate initramfs misc nfs rasdaemon selinux unbound 7 bluetooth dhclient games iscsi mlocate os-prober rhsm setroubleshoot upower 8 boltd dnsmasq gdm kubelet mysql PackageKit rpcbind stateless vmware 9 chrony docker geoclue libvirt mysql-files plymouth rpm systemd xkb 10 [root@k8s-node3 lib]# ls mysql mysql- 11 mysql-files/ mysql-keyring/ 12 [root@k8s-node3 lib]# ls mysql mysql- 13 mysql-files/ mysql-keyring/ 14 [root@k8s-node3 lib]# ls mysql mysql-files/ mysql-keyring/ 15 mysql: 16 17 mysql-files/: 18 19 mysql-keyring/: 20 [root@k8s-node3 lib]#
在/var/log/ 下可以看到 mysqld.log 文件，如下所示：
1 [root@k8s-node3 lib]# cd /var/lo 2 local/ lock/ log/ 3 [root@k8s-node3 lib]# cd /var/log/ 4 [root@k8s-node3 log]# ls 5 anaconda cron libvirt qemu-ga spooler-20200714 vmware-vgauthsvc.log.0 6 audit cron-20200618 maillog rhsm swtpm vmware-vmsvc.log 7 boot.log cron-20200625 maillog-20200618 sa tallylog vmware-vmusr.log 8 boot.log-20200618 cron-20200628 maillog-20200625 samba tuned wpa_supplicant.log 9 boot.log-20200622 cron-20200714 maillog-20200628 secure vmware-network.1.log wtmp 10 boot.log-20200629 cups maillog-20200714 secure-20200618 vmware-network.2.log Xorg.0.log 11 boot.log-20200630 dmesg messages secure-20200625 vmware-network.3.log Xorg.0.log.old 12 boot.log-20200702 dmesg.old messages-20200618 secure-20200628 vmware-network.4.log Xorg.9.log 13 boot.log-20200703 firewalld messages-20200625 secure-20200714 vmware-network.5.log yum.log 14 boot.log-20200714 gdm messages-20200628 speech-dispatcher vmware-network.6.log 15 btmp gitlab messages-20200714 spooler vmware-network.7.log 16 btmp-20200702 glusterfs mysqld.log spooler-20200618 vmware-network.8.log 17 chrony grubby_prune_debug pluto spooler-20200625 vmware-network.9.log 18 containers lastlog ppp spooler-20200628 vmware-network.log 19 [root@k8s-node3 log]# ll mysqld.log 20 -rw-r----- 1 mysql mysql 0 Jul 15 14:17 mysqld.log 21 [root@k8s-node3 log]#
在/var/run/ 下可以看到 mysqld 目录，如下所示：
1 [root@k8s-node3 log]# cd /var/run/ 2 [root@k8s-node3 run]# ls 3 abrt cups gitlab lock NetworkManager setrans udev 4 alsactl.pid dbus gluster log plymouth setroubleshoot udisks2 5 atd.pid dmeventd-client glusterd.pid lsm ppp sm-notify.pid user 6 auditd.pid dmeventd-server glusterd.socket lvm radvd spice-vdagentd utmp 7 avahi-daemon docker gssproxy.pid lvmetad.pid rhsm sshd.pid vmware 8 blkid docker.pid gssproxy.sock mcelog-client rpcbind sudo xtables.lock 9 console docker.sock initramfs mcelog.pid rpcbind.lock sysconfig 10 container-storage-setup ebtables.lock ksmtune.pid mdadm rpcbind.sock syslogd.pid 11 crond.pid faillock kubernetes mount runc systemd 12 cron.reboot flannel libvirt mysqld samba tmpfiles.d 13 cryptsetup gdm libvirtd.pid netreport sepermit tuned 14 [root@k8s-node3 run]# ls mysqld/ 15 [root@k8s-node3 run]# ll mysqld/ 16 total 0 17 [root@k8s-node3 run]#
3、登录并创建 mysql 密码，启动mysql，安装完后，使用命令 service mysqld start 或 systemctl start mysqld.service 启动MySQL服务，如果mysql服务无法启动，就重启一下系统。
1 [root@k8s-node3 ~]# systemctl start mysqld.service 2 [root@k8s-node3 ~]# systemctl status mysqld.service 3 ● mysqld.service - MySQL Server 4 Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled) 5 Active: active (running) since Wed 2020-07-15 14:23:18 CST; 11s ago 6 Docs: man:mysqld(8) 7 http://dev.mysql.com/doc/refman/en/using-systemd.html 8 Process: 129166 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS) 9 Process: 129095 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS) 10 Main PID: 129169 (mysqld) 11 Tasks: 27 12 Memory: 259.3M 13 CGroup: /system.slice/mysqld.service 14 └─129169 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid 15 16 Jul 15 14:23:12 k8s-node3 systemd[1]: Starting MySQL Server... 17 Jul 15 14:23:18 k8s-node3 systemd[1]: Started MySQL Server. 18 [root@k8s-node3 ~]#
启动、停止、查看状态命令如下所示：
1 systemctl start mysqld.service # 此命令是启动mysql 2 systemctl status mysqld.service # 此命令是查看mysql状态 3 systemctl stop mysqld.service # 此命令是关闭mysql
查看mysql进程 ps -ef | grep mysql，查看3306端口 netstat -anop | grep 3306。
1 [root@k8s-node3 ~]# ps -ef | grep mysql 2 mysql 129169 1 0 14:23 ? 00:00:00 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid 3 root 129514 121741 0 14:25 pts/2 00:00:00 grep --color=auto mysql 4 [root@k8s-node3 ~]# netstat -nultp | grep 3306 5 tcp6 0 0 :::3306 :::* LISTEN 129169/mysqld 6 [root@k8s-node3 ~]#
登陆mysql修改root密码，由于MySQL5.7.4之前的版本中默认是没有密码的，登录后直接回车就可以进入数据库，进而进行设置密码等操作。其后版本对密码等安全相关操作进行了一些改变，在安装过程中，会在安装日志中生成一个临时密码。使用命令grep 'temporary password' /var/log/mysqld.log找到这个临时密码。
1 [root@k8s-node3 ~]# grep 'temporary password' /var/log/mysqld.log 2 2020-07-15T06:23:15.406927Z 1 [Note] A temporary password is generated for root@localhost: OUvw#frSq7iI 3 [root@k8s-node3 ~]#
即可查询到类似于如下的一条日志记录，如下所示：
1 [root@k8s-node3 ~]# grep 'temporary password' /var/log/mysqld.log 2 2020-07-15T06:23:15.406927Z 1 [Note] A temporary password is generated for root@localhost: OUvw#frSq7iI 3 [root@k8s-node3 ~]#
OUvw#frSq7iI即为登录密码。使用这个随机密码登录进去，然后修改密码，如下所示：
1 [root@k8s-node3 ~]# grep 'temporary password' /var/log/mysqld.log
2 2020-07-15T06:23:15.406927Z 1 [Note] A temporary password is generated for root@localhost: OUvw#frSq7iI
3 [root@k8s-node3 ~]# mysql -uroot -p
4 Enter password:
5 Welcome to the MySQL monitor. Commands end with ; or \g.
6 Your MySQL connection id is 2
7 Server version: 5.7.30
8
9 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
10
11 Oracle is a registered trademark of Oracle Corporation and/or its
12 affiliates. Other names may be trademarks of their respective
13 owners.
14
15 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
16
17 mysql> set password for root@localhost=password('123456');
18 ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
19 mysql> set global validate_password_policy=0; # 此时，新密码长度大于等于8位才有效，否则报错
20 Query OK, 0 rows affected (0.00 sec)
21
22 mysql> set global validate_password_length=1; # 修改有效密码长度。
23 Query OK, 0 rows affected (0.00 sec)
24
25 mysql> set password for root@localhost=password('123456');
26 Query OK, 0 rows affected, 1 warning (0.01 sec)
27
28 mysql>
执行下面的命令set password for root@localhost=password('123456');修改MySql root密码，但是在5.6后,mysql内置密码增强机制,低强度密码会报错:ERROR 1819 (HY000): Your password does not satisfy the current policy requirements。
1 第一步是，更改策略，设置 validate_password_policy=0;
2 mysql> set global validate_password_policy=0; # 此时，新密码长度大于等于8位才有效，否则报错
3
4 然后修改有效密码长度：
5 mysql> set global validate_password_length=1;
6 不管设置 validate_password_length=1,还是2,3,4 ,"使密码长度生效"这个参数的实际值都是4。超过4后设置是多少实际就是多少。
7
8 第二步就可以重新设置密码了，如下所示：
9 mysql> set password for root@localhost=password('123456');
10 Query OK, 0 rows affected, 1 warning (0.01 sec)
使用修改之后的密码就可以顺利登录，如下所示：
1 [root@k8s-node3 ~]# mysql -uroot -p123456 2 mysql: [Warning] Using a password on the command line interface can be insecure. 3 Welcome to the MySQL monitor. Commands end with ; or \g. 4 Your MySQL connection id is 3 5 Server version: 5.7.30 MySQL Community Server (GPL) 6 7 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 8 9 Oracle is a registered trademark of Oracle Corporation and/or its 10 affiliates. Other names may be trademarks of their respective 11 owners. 12 13 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 14 15 mysql>
此时，虽然防火墙我时关着的，但root用户只能用于本机访问，不能用于远程访问，否则会报以下错误。因此，接下来要做的是授予root用户远程访问权限。
查看当前授予过的权限，如下所示：
1 [root@k8s-node3 ~]# mysql -uroot -p123456 2 mysql: [Warning] Using a password on the command line interface can be insecure. 3 Welcome to the MySQL monitor. Commands end with ; or \g. 4 Your MySQL connection id is 3 5 Server version: 5.7.30 MySQL Community Server (GPL) 6 7 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 8 9 Oracle is a registered trademark of Oracle Corporation and/or its 10 affiliates. Other names may be trademarks of their respective 11 owners. 12 13 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 14 15 mysql> use mysql; 16 Reading table information for completion of table and column names 17 You can turn off this feature to get a quicker startup with -A 18 19 Database changed 20 mysql> select user,host from user; 21 +---------------+-----------+ 22 | user | host | 23 +---------------+-----------+ 24 | mysql.session | localhost | 25 | mysql.sys | localhost | 26 | root | localhost | 27 +---------------+-----------+ 28 3 rows in set (0.00 sec) 29 30 mysql> grant all privileges on *.* to root@'%' identified by '123456'; # 授予root用户远程访问权限。 31 Query OK, 0 rows affected, 1 warning (0.00 sec) 32 33 mysql> flush privileges; # 刷新权限，使设置生效。 34 Query OK, 0 rows affected (0.00 sec) 35 36 mysql>
现在可以远程链接服务器上面的mysql数据库，如下所示：
4、验证mysql安装成功，如下所示：
1 [root@k8s-node3 ~]# mysqladmin --version 2 mysqladmin Ver 8.42 Distrib 5.7.30, for Linux on x86_64 3 [root@k8s-node3 ~]#
查看mysql检查是否开机自启动，服务前面存在*的是开机自启动的，没有*的是开机不自启动的，如下所示：
1 [root@k8s-node3 ~]# ntsysv 2 3 ntsysv 1.7.4 - (C) 2000-2001 Red Hat, Inc. 4 5 6 ─┐ 7 │ 8 What services should be automatically started? │ 9 │ 10 [*] mdmonitor.service ↑ │ 11 [*] microcode.service ? │ 12 [*] multipathd.service ? │ 13 [*] mysqld.service ? │ 14 [ ] ndctl-monitor.service ? │ 15 [ ] netcf-transaction.service ? │ 16 [ ] nfs-blkmap.service ? │ 17 [ ] nfs-rquotad.service ? │ 18 [ ] nfs-server.service ? │ 19 [ ] nfs.service ↓ │ 20 │ 21 ┌────┐ ┌────────┐ │ 22 │ Ok │ │ Cancel │ │ 23 └────┘ └────────┘ │ 24 │ 25 │ │ 26 └──────────────────────────────────────────────────┘ 27 28 29 Pressfor more information on a service.
mysql的核心目录，如下所示：
1 1）、/var/lib/mysql，mysql的安装目录。 2 2）、/usr/share/mysql/，mysql的配置文件。 3 3）、/usr/bin/，mysql的命令目录。 4 5 6 [root@k8s-node3 ~]# ls /var/lib/mysql 7 auto.cnf client-cert.pem ibdata1 ibtmp1 mysql.sock.lock public_key.pem sys 8 ca-key.pem client-key.pem ib_logfile0 mysql performance_schema server-cert.pem 9 ca.pem ib_buffer_pool ib_logfile1 mysql.sock private_key.pem server-key.pem 10 [root@k8s-node3 ~]# ls /usr/share/mysql/ 11 bulgarian french mysql-log-rotate romanian 12 charsets german mysql_security_commands.sql russian 13 czech greek mysql_sys_schema.sql serbian 14 danish hungarian mysql_system_tables_data.sql slovak 15 dictionary.txt innodb_memcached_config.sql mysql_system_tables.sql spanish 16 dutch install_rewriter.sql mysql_test_data_timezone.sql swedish 17 english italian norwegian ukrainian 18 errmsg-utf8.txt japanese norwegian-ny uninstall_rewriter.sql 19 estonian korean polish 20 fill_help_tables.sql magic portuguese 21 [root@k8s-node3 ~]# ls /usr/bin/
5、查看Mysql的字符集编码，如下所示：
1 [root@k8s-node3 ~]# mysql -uroot -p123456 2 mysql: [Warning] Using a password on the command line interface can be insecure. 3 Welcome to the MySQL monitor. Commands end with ; or \g. 4 Your MySQL connection id is 4 5 Server version: 5.7.30 MySQL Community Server (GPL) 6 7 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 8 9 Oracle is a registered trademark of Oracle Corporation and/or its 10 affiliates. Other names may be trademarks of their respective 11 owners. 12 13 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 14 15 mysql> show variables like '%char%'; 16 +--------------------------------------+----------------------------+ 17 | Variable_name | Value | 18 +--------------------------------------+----------------------------+ 19 | character_set_client | utf8 | 20 | character_set_connection | utf8 | 21 | character_set_database | latin1 | 22 | character_set_filesystem | binary | 23 | character_set_results | utf8 | 24 | character_set_server | latin1 | 25 | character_set_system | utf8 | 26 | character_sets_dir | /usr/share/mysql/charsets/ | 27 | validate_password_special_char_count | 1 | 28 +--------------------------------------+----------------------------+ 29 9 rows in set (0.00 sec) 30 31 mysql>
设置字符集编码为utf8格式的，如下所示：
1 # For advice on how to change settings please see 2 # http://dev.mysql.com/doc/refman/5.7/en/server-configuration-defaults.html 3 4 [mysqld] 5 init_connect='SET NAMES utf8' 6 character-set-server=utf8 7 # character_set_client=utf8 8 collation-server=utf8_general_ci 9 # 10 # Remove leading # and set to the amount of RAM for the most important data 11 # cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%. 12 # innodb_buffer_pool_size = 128M 13 # 14 # Remove leading # to turn on a very important data integrity option: logging 15 # changes to the binary log between backups. 16 # log_bin 17 # 18 # Remove leading # to set options mainly useful for reporting servers. 19 # The server defaults are faster for transactions and fast SELECTs. 20 # Adjust sizes as needed, experiment to find the optimal values. 21 # join_buffer_size = 128M 22 # sort_buffer_size = 2M 23 # read_rnd_buffer_size = 2M 24 datadir=/var/lib/mysql 25 socket=/var/lib/mysql/mysql.sock 26 27 # Disabling symbolic-links is recommended to prevent assorted security risks 28 symbolic-links=0 29 30 log-error=/var/log/mysqld.log 31 pid-file=/var/run/mysqld/mysqld.pid 32 33 [mysql] 34 default-character-set=utf8 35 36 [mysql_safe] 37 default-character-set=utf8 38 "my.cnf" 41L, 1192C
修改内容，如下所示：
此时，需要重启mysql的，如下所示：
1 [root@k8s-node3 etc]# systemctl restart mysqld.service 2 [root@k8s-node3 etc]# systemctl status mysqld.service 3 ● mysqld.service - MySQL Server 4 Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled) 5 Active: active (running) since Wed 2020-07-15 18:49:25 CST; 2s ago 6 Docs: man:mysqld(8) 7 http://dev.mysql.com/doc/refman/en/using-systemd.html 8 Process: 26346 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS) 9 Process: 26322 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS) 10 Main PID: 26349 (mysqld) 11 Tasks: 27 12 Memory: 218.8M 13 CGroup: /system.slice/mysqld.service 14 └─26349 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid 15 16 Jul 15 18:49:23 k8s-node3 systemd[1]: Starting MySQL Server... 17 Jul 15 18:49:25 k8s-node3 systemd[1]: Started MySQL Server.
再次查看字符集编码，如下所示：
1 mysql> SHOW VARIABLES LIKE 'character_set_%'; 2 +--------------------------+----------------------------+ 3 | Variable_name | Value | 4 +--------------------------+----------------------------+ 5 | character_set_client | utf8 | 6 | character_set_connection | utf8 | 7 | character_set_database | utf8 | 8 | character_set_filesystem | binary | 9 | character_set_results | utf8 | 10 | character_set_server | utf8 | 11 | character_set_system | utf8 | 12 | character_sets_dir | /usr/share/mysql/charsets/ | 13 +--------------------------+----------------------------+ 14 8 rows in set (0.01 sec) 15 16 mysql> SHOW VARIABLES LIKE 'collation_%'; 17 +----------------------+-----------------+ 18 | Variable_name | Value | 19 +----------------------+-----------------+ 20 | collation_connection | utf8_general_ci | 21 | collation_database | utf8_general_ci | 22 | collation_server | utf8_general_ci | 23 +----------------------+-----------------+ 24 3 rows in set (0.01 sec) 25 26 mysql>
注意，修改字符集编码，只对后面创建的数据库生效，之前创建的数据库字符集还是保持之前的不发生变化。
6、Mysql的命令行清屏命令system clear或者ctrl + L命令，如下所示：
1 mysql> system clear 2 mysql>
mysql的逻辑分层，分别是连接层、服务层、引擎层、存储层，如下所示：
查看mysql的存储引擎，首先查看mysql支持的引擎，如下所示：
1 [root@k8s-node3 ~]# mysql -uroot -p123456 2 mysql: [Warning] Using a password on the command line interface can be insecure. 3 Welcome to the MySQL monitor. Commands end with ; or \g. 4 Your MySQL connection id is 5 5 Server version: 5.7.30 MySQL Community Server (GPL) 6 7 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 8 9 Oracle is a registered trademark of Oracle Corporation and/or its 10 affiliates. Other names may be trademarks of their respective 11 owners. 12 13 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 14 15 mysql> show engines; 16 +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 17 | Engine | Support | Comment | Transactions | XA | Savepoints | 18 +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 19 | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | 20 | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | 21 | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | 22 | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | 23 | MyISAM | YES | MyISAM storage engine | NO | NO | NO | 24 | CSV | YES | CSV storage engine | NO | NO | NO | 25 | ARCHIVE | YES | Archive storage engine | NO | NO | NO | 26 | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | 27 | FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL | 28 +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 29 9 rows in set (0.01 sec) 30 31 mysql>
查看当前Mysql的存储引擎，如下所示：
1 mysql> show variables like '%storage_engine%'; 2 +----------------------------------+--------+ 3 | Variable_name | Value | 4 +----------------------------------+--------+ 5 | default_storage_engine | InnoDB | 6 | default_tmp_storage_engine | InnoDB | 7 | disabled_storage_engines | | 8 | internal_tmp_disk_storage_engine | InnoDB | 9 +----------------------------------+--------+ 10 4 rows in set (0.00 sec) 11 12 mysql>
查看某个数据表使用了什么存储引擎，在显示结果里参数engine后面的就表示该表当前用的存储引擎。
1 mysql> show create table user_info; 2 +-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 3 | Table | Create Table | 4 +-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 5 | user_info | CREATE TABLE `user_info` ( 6 `user_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '用户编号', 7 `user_account` varchar(15) DEFAULT NULL COMMENT '用户账号', 8 `user_pw` varchar(15) DEFAULT NULL COMMENT '用户密码', 9 `user_number` varchar(15) DEFAULT NULL COMMENT '用户手机号', 10 `user_name` varchar(10) DEFAULT NULL COMMENT '用户姓名', 11 `user_age` int(11) DEFAULT NULL COMMENT '用户年龄', 12 `user_sex` varchar(5) DEFAULT NULL COMMENT '用户性别', 13 `user_mark` varchar(5) DEFAULT NULL COMMENT '用户标志', 14 `create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '用户创建时间', 15 `is_sync` int(3) DEFAULT '0' COMMENT '用户标识', 16 `is_money` varchar(255) DEFAULT NULL COMMENT '是否缴纳押金', 17 PRIMARY KEY (`user_id`) USING BTREE, 18 KEY `user_id` (`user_id`) USING BTREE 19 ) ENGINE=InnoDB AUTO_INCREMENT=42 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC COMMENT='用户信息表' | 20 +-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 21 1 row in set (0.00 sec) 22 23 mysql>
7、mysql的sql优化，原因可能是性能低，执行时间太长，等待时间太长，sql语句欠佳，比如连接查询，索引失效，服务器参数设置不佳。
Sql的编写过程、解析过程，如下所示：
1 编写过程：select distinct ... from ... join ... on ... where ... group by ... having ... order by ... limit ... 2 解析过程：from ... on ... join ... where ... group by ... having ... select distinct ... order by ... limit ...
SQL优化，主要就是在于优化索引，索引相当于是书的目录。索引，index是帮助Mysql高效获取数据的数据结构，索引是数据结构（树，常见的B树，默认是B树，Hash树）。
索引的弊端，索引本身很大，可以存放在内存或者硬盘中，通常为硬盘。索引不是所有情况均适用的，如果是少量数据不适用。如果是频繁更新的字段不适用。很少使用的列也不适合添加索引。索引会降低增删改的效率，提高查询的效率。
索引的优点，提高查询效率，降低IO使用率，降低CPU使用率，因为B树索引本事就是一个排好序的结构，因此在排序的时候，可以直接使用的。
8、mysql如何进行优化呢，查看使用索引的情况，查询执行计划，explain + SQL语句。
1 mysql> explain select * from book_info; 2 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------+ 5 | 1 | SIMPLE | book_info | NULL | ALL | NULL | NULL | NULL | NULL | 16 | 100.00 | NULL | 6 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------+ 7 1 row in set, 1 warning (0.01 sec)
详细信息介绍，如下所示：
1 id ：编号 2 select_type ：查询类型 3 table ：数据表，指的查询的那张表。 4 partitions ： 5 type ：类型 6 possible_keys ： 预测使用到的索引 7 key ：实际使用的索引 8 key_len ： 实际使用索引的长度 9 ref ： 表之间的引用 10 rows ： 通过索引查询到的数据量 11 filtered ： 12 Extra ：额外的信息
8.1、id编号的用法，多表关联查询（备注：多表联查都可以转换为子查询得到想要的结果）特点：
1）、id编号值相同，数据小的表，优先查询。
2）、如果是id编号值不同，id编号值越大越优先查询（执行本质，在嵌套子查询的时候，先查询内层，再查询外层）。
3）、id值有相同，又有不同，id值越大越优先。id值相同从上往下，顺序执行。这里的id编号指定的是explain的查询结果字段id哦。
1 mysql> explain 2 -> select * from book_info bi,book_sort bs WHERE bi.book_sort_id = bs.book_sort_id and bi.book_name = 'Java'; 3 +----+-------------+-------+------------+--------+------------------------+-----------+---------+----------------------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+--------+------------------------+-----------+---------+----------------------+------+----------+-------------+ 6 | 1 | SIMPLE | bi | NULL | ref | book_sort_id,book_name | book_name | 48 | const | 1 | 100.00 | Using where | 7 | 1 | SIMPLE | bs | NULL | eq_ref | PRIMARY | PRIMARY | 4 | book.bi.book_sort_id | 1 | 100.00 | NULL | 8 +----+-------------+-------+------------+--------+------------------------+-----------+---------+----------------------+------+----------+-------------+ 9 2 rows in set, 1 warning (0.00 sec) 10 11 mysql>
1 mysql> explain 2 -> select * from book_info bi WHERE bi.book_sort_id = (SELECT book_sort_id from book_sort bs WHERE bs.book_sort_name = '自然科学总论') 3 -> ; 4 +----+-------------+-------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ 5 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 6 +----+-------------+-------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ 7 | 1 | PRIMARY | bi | NULL | ref | book_sort_id | book_sort_id | 5 | const | 2 | 100.00 | Using where | 8 | 2 | SUBQUERY | bs | NULL | ALL | NULL | NULL | NULL | NULL | 21 | 10.00 | Using where | 9 +----+-------------+-------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ 10 2 rows in set, 1 warning (0.00 sec) 11 12 mysql>
8.2）、select_type查询类型的用法，如下所示：
1）、PRIMARY：包含子查询SQL中的主查询，一般是SQL嵌套的最外层。
2）、SUBQUERY：包含子查询SQL中的子查询，一般是SQL嵌套的非最外层。
3）、SIMPLE：简单查询，不包含子查询，不包含union查询。
4）、DERIVED：衍生查询。在查询的时候使用到了临时表。两种情况，第一种是from子查询中只有一张表。第二种是在from子查询中，如果有两张表table1 union table2连接查询，则table1这个左表就是衍生查询。
1 mysql> explain
2 -> SELECT b.book_name from (SELECT * from book_info WHERE book_name in ('Java') UNION SELECT * from book_info WHERE book_name in ('python') ) b;
3 +----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
5 +----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
6 | 1 | PRIMARY | | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 100.00 | NULL |
7 | 2 | DERIVED | book_info | NULL | ALL | NULL | NULL | NULL | NULL | 16 | 10.00 | Using where |
8 | 3 | UNION | book_info | NULL | ALL | NULL | NULL | NULL | NULL | 16 | 10.00 | Using where |
9 | NULL | UNION RESULT | | NULL | ALL | NULL | NULL | NULL | NULL | NULL | NULL | Using temporary |
10 +----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
11 4 rows in set, 1 warning (0.00 sec)
12
13 mysql>
DERIVED代表了衍生表，table的值是derived2代表了是主查询涉及到衍生表，而2代表了指明了id编号是2，代表了衍生了那张表，临时表是从id为2的这个table是book_info来的。
8.3）、type成为索引类型，或者称为类型。system > const > eq_ref > ref > index > all，其中性能由左向右依次降低，但是system、const只是理想状态，实际可以达到的一般是ref、range。
1）、system，只有一条数据的系统表，基本达不到，或者衍生表只有一条数据的主查询，偶尔可以达到。
2）、const，仅仅可以查询到一条数据的sql，并且用于Primary key或者unique索引的时候就是const。必须针对Primary key或者unique索引的时候，与索引类型有关。
3）、eq_ref，唯一性索引，对于每个索引键的查询，返回匹配唯一行数据，唯一的意思是有且只有一个，不能多也不能为0。常见于唯一索引和主键索引。
4）、ref，非唯一性索引，对于每个索引键的查询，返回匹配的所有行（可以是0个或者多个）。
5）、range，检索指定范围的行，具体就是where后面是一个范围查询，比如between and、in、>、<等等。特殊的in有时候会失效，从而转换为无索引All，即in范围查询会导致索引失效，可以将in范围查询放到字段查询的后面。
6）、index，查询全部索引的数据。只需要扫描索引表，不需要扫描全部数据。
7）、all，查询全部表中数据。需要扫描全表，即需要所有表中的所有数据。
1 mysql> explain select * from book_info where book_id > 5; 2 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 5 | 1 | SIMPLE | book_info | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 13 | 100.00 | Using where | 6 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 7 1 row in set, 1 warning (0.00 sec)
8.4）、possible_keys，可能用到的索引，是一种预测，不准。
8.5）、key，实际使用到的索引。如果possible_keys或者key为NULL，说明没有使用到索引。
1 mysql> explain select * from book_info where book_id > 5; 2 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 5 | 1 | SIMPLE | book_info | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 13 | 100.00 | Using where | 6 +----+-------------+-----------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 7 1 row in set, 1 warning (0.00 sec)
8.6）、key_len，索引的长度。作用就是用于判断复合索引是否被完全使用。
1）、utf8中，一个字符占用三个字节。如果索引字段可以为null，则会使用1个字节用于标识。如果是固定长度char就是char(n)中的n乘以三，如果可以为null，再加一即可。
2）、utf8中，一个字符占用三个字节。如果索引字段可以为null，则会使用1个字节用于标识。如果是可变长度varchar，就是varchar(n)中的n乘以三，如果可以为null，再加一，然后varhar是可变长度，然后再加二，用两个字节来表示可变长度。比如book_name是varchar(15)，15 * 3 + 1 + 2 = 48。如果是复合索引，book_type是varchar(200)，组合book_name是varchar(15)，就是200 * 3 + 1 + 2 + 15 * 3 + 1 + 2 = 651。
1 mysql> EXPLAIN 2 -> SELECT * from book_info WHERE book_name = 'Java' and book_type = '自然科学总论'; 3 +----+-------------+-----------+------------+------+-----------------------------------------+-----------+---------+-------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+------+-----------------------------------------+-----------+---------+-------+------+----------+-------------+ 6 | 1 | SIMPLE | book_info | NULL | ref | book_type,book_name,book_name_book_type | book_name | 48 | const | 1 | 12.50 | Using where | 7 +----+-------------+-----------+------------+------+-----------------------------------------+-----------+---------+-------+------+----------+-------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql> EXPLAIN 11 -> SELECT * from book_info WHERE book_name = 'Java' and book_type = '自然科学总论'; 12 +----+-------------+-----------+------------+------+-------------------------------+---------------------+---------+-------------+------+----------+-------+ 13 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 14 +----+-------------+-----------+------------+------+-------------------------------+---------------------+---------+-------------+------+----------+-------+ 15 | 1 | SIMPLE | book_info | NULL | ref | book_type,book_name_book_type | book_name_book_type | 651 | const,const | 1 | 100.00 | NULL | 16 +----+-------------+-----------+------------+------+-------------------------------+---------------------+---------+-------------+------+----------+-------+ 17 1 row in set, 1 warning (0.00 sec) 18 19 mysql>
注意：utf8是一个字符三个节点，gbk是一个字符两个字节，latin是一个字符一个字节。
8.7）、ref，注意与type中的ref值进行区分，作用是指明当前表所参照的字段。如果是常量，值就是const。
1 mysql> EXPLAIN 2 -> SELECT bi.* from book_info bi,book_sort bs WHERE bi.book_sort_id = bs.book_sort_id and bi.book_name = 'Java'; 3 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 6 | 1 | SIMPLE | bi | NULL | ref | book_sort_id,book_name_book_type | book_name_book_type | 48 | const | 1 | 100.00 | Using where | 7 | 1 | SIMPLE | bs | NULL | eq_ref | PRIMARY | PRIMARY | 4 | book.bi.book_sort_id | 1 | 100.00 | Using index | 8 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 9 2 rows in set, 1 warning (0.00 sec) 10 11 mysql>
8.8）、rows，被索引优化查询的数据个数。
1 mysql> EXPLAIN 2 -> SELECT bi.* from book_info bi,book_sort bs WHERE bi.book_sort_id = bs.book_sort_id and bi.book_name = 'Java'; 3 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 6 | 1 | SIMPLE | bi | NULL | ref | book_sort_id,book_name_book_type | book_name_book_type | 48 | const | 1 | 100.00 | Using where | 7 | 1 | SIMPLE | bs | NULL | eq_ref | PRIMARY | PRIMARY | 4 | book.bi.book_sort_id | 1 | 100.00 | Using index | 8 +----+-------------+-------+------------+--------+----------------------------------+---------------------+---------+----------------------+------+----------+-------------+ 9 2 rows in set, 1 warning (0.00 sec)
8.9）、Extra，就是额外的，剩下的意思，常见的有using filesort（出现这种情况要避免）、Using temporary（出现这种情况要避免）、Using where、Using index。
1）、using filesort：表示性能低，消耗比较大，当前的sql语句需要额外的一次排序查询。理解起来就是先根据这个字段查询，然后根据这个字段排序。如果是先根据一个字段查询，根据另外一个字段排序，那么当前的sql语句需要额外的一次排序查询。常见于order by语句中。
1 mysql> SELECT * from book_info WHERE book_name = 'Java' ORDER BY book_name; 2 +---------+--------------+-----------+-------------+------------+--------------------+-----------------+----------+-----------+---------------------+------------+-------------------------------------+ 3 | book_id | book_sort_id | book_name | book_author | book_price | book_type | book_publish | book_sum | book_mark | create_time | book_money | book_desc | 4 +---------+--------------+-----------+-------------+------------+--------------------+-----------------+----------+-----------+---------------------+------------+-------------------------------------+ 5 | 3 | 19 | Java | 别先生 | 29.90 | 自然科学总论 | 科学出版社 | 6 | NULL | 2019-02-15 19:09:45 | 199.00 |Java大神如何练成的？
| 6 +---------+--------------+-----------+-------------+------------+--------------------+-----------------+----------+-----------+---------------------+------------+-------------------------------------+ 7 1 row in set (0.00 sec) 8 9 mysql> EXPLAIN 10 -> SELECT * from book_info WHERE book_name = 'Java' ORDER BY book_author; 11 +----+-------------+-----------+------------+------+---------------------+---------------------+---------+-------+------+----------+---------------------------------------+ 12 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 13 +----+-------------+-----------+------------+------+---------------------+---------------------+---------+-------+------+----------+---------------------------------------+ 14 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type | book_name_book_type | 48 | const | 1 | 100.00 | Using index condition; Using filesort | 15 +----+-------------+-----------+------------+------+---------------------+---------------------+---------+-------+------+----------+---------------------------------------+ 16 1 row in set, 1 warning (0.00 sec) 17 18 mysql>
总结：对于单索引，如果排序和查找是同一字段，则不会出现using filesort，如果排序和查找不是同一字段，则会出现using filesort。
对于复合索引，不能跨列（最佳左前缀，即从左到右依次使用，不能跨列使用，比如三个字段的索引，不能跨过第二个索引）。where和order by按照复合索引的顺序使用，不要跨列或者无序使用。
1 mysql> EXPLAIN 2 -> SELECT * from book_info WHERE book_name = 'Java' ORDER BY book_author; 3 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+---------------------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+---------------------------------------+ 6 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type_book_author | book_name_book_type_book_author | 48 | const | 1 | 100.00 | Using index condition; Using filesort | 7 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+---------------------------------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql> EXPLAIN 11 -> SELECT * from book_info WHERE book_name = 'Java' ORDER BY book_type; 12 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-----------------------+ 13 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 14 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-----------------------+ 15 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type_book_author | book_name_book_type_book_author | 48 | const | 1 | 100.00 | Using index condition | 16 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-----------------------+ 17 1 row in set, 1 warning (0.00 sec) 18 19 mysql>
2）、Using temporary：性能损耗大，用到了临时表。一般出现在group by的语句中。如何避免？查询那些列，就根据那些列进行group by进行分组。出现的原因就是已经有表了，但是不使用，必须再来一张临时表进行分组查询出结果。
1 mysql> EXPLAIN 2 -> SELECT book_name from book_info WHERE book_name = 'Java' GROUP BY book_name; 3 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 6 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type_book_author | book_name_book_type_book_author | 48 | const | 1 | 100.00 | Using index | 7 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql> EXPLAIN 11 -> SELECT book_name from book_info WHERE book_name = 'Java' GROUP BY book_publish; 12 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+--------------------------------------------------------+ 13 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 14 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+--------------------------------------------------------+ 15 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type_book_author | book_name_book_type_book_author | 48 | const | 1 | 100.00 | Using index condition; Using temporary; Using filesort | 16 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+--------------------------------------------------------+ 17 1 row in set, 1 warning (0.00 sec) 18 19 mysql>
重点，解析过程：from ... on ... join ... where ... group by ... having ... select distinct ... order by ... limit ...
3）、Using index：表示性能提升了，意思是索引覆盖，原因在于不读取原文件，只从索引文件中获取数据，不需要回表查询。只要使用到的列全部都在索引中，就是索引覆盖Using index。只要使用到的列不都在索引中，就不会出现索引覆盖Using index。
1 mysql> EXPLAIN 2 -> SELECT book_name from book_info WHERE book_name = 'Java'; 3 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 6 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_type_book_author | book_name_book_type_book_author | 48 | const | 1 | 100.00 | Using index | 7 +----+-------------+-----------+------------+------+---------------------------------+---------------------------------+---------+-------+------+----------+-------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql> EXPLAIN 11 -> SELECT book_name from book_info WHERE book_name = 'Java' or book_type = '自然科学总论'; 12 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 13 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 14 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 15 | 1 | SIMPLE | book_info | NULL | index | book_type,book_name_book_type_book_author | book_name_book_type_book_author | 699 | NULL | 16 | 19.00 | Using where; Using index | 16 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 17 1 row in set, 1 warning (0.00 sec) 18 19 mysql> EXPLAIN 20 -> SELECT book_name from book_info WHERE book_type = '自然科学总论' or book_name = 'Java' ; 21 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 22 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 23 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 24 | 1 | SIMPLE | book_info | NULL | index | book_type,book_name_book_type_book_author | book_name_book_type_book_author | 699 | NULL | 16 | 19.00 | Using where; Using index | 25 +----+-------------+-----------+------------+-------+-------------------------------------------+---------------------------------+---------+------+------+----------+--------------------------+ 26 1 row in set, 1 warning (0.00 sec) 27 28 mysql>
如果用到了索引覆盖，索引覆盖Using index会对possible_keys、key造成影响，如果没有where，则索引只出现在key中，如果有where，则索引出现在key和possible_keys中。
1 mysql> EXPLAIN SELECT book_name from book_info; 2 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+-------------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+-------------+ 5 | 1 | SIMPLE | book_info | NULL | index | NULL | book_name_book_author | 96 | NULL | 16 | 100.00 | Using index | 6 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+-------------+ 7 1 row in set, 1 warning (0.00 sec) 8 9 10 mysql> EXPLAIN SELECT book_name from book_info WHERE book_name = '自然科学总论'; 11 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------+------+----------+-------------+ 12 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 13 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------+------+----------+-------------+ 14 | 1 | SIMPLE | book_info | NULL | ref | book_name_book_author | book_name_book_author | 48 | const | 1 | 100.00 | Using index | 15 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------+------+----------+-------------+ 16 1 row in set, 1 warning (0.00 sec) 17 18 mysql>
4）、Using where：表示需要从原表中查询。即需要回表查询的。
1 mysql> EXPLAIN 2 -> SELECT book_name,book_type from book_info WHERE book_type = 'Java' ; 3 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+ 6 | 1 | SIMPLE | book_info | NULL | ALL | NULL | NULL | NULL | NULL | 16 | 10.00 | Using where | 7 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+ 8 1 row in set, 1 warning (0.01 sec) 9 10 mysql>
5）、impossibal where，where子句永远为false。
1 mysql> EXPLAIN 2 -> SELECT book_name,book_type from book_info WHERE book_type = 'Java' AND book_type = 'Python' ; 3 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ 6 | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE | 7 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ 8 1 row in set, 1 warning (0.01 sec) 9 10 mysql>
条件字段的顺序最好和组合索引的顺序一致，如果不一致，SQL优化器可以会对sql进行优化，使用到索引，但是强烈推荐保持条件字段顺序和组合索引顺序一致。如果复合索引和使用的顺序一致（且不跨列使用），则复合索引全部使用，如果部分一致，则使用部分索引。
9、mysql的单表索引优化案例，如下所示：
1 SET NAMES utf8mb4; 2 SET FOREIGN_KEY_CHECKS = 0; 3 4 -- ---------------------------- 5 -- Table structure for user_info 6 -- ---------------------------- 7 DROP TABLE IF EXISTS `user_info`; 8 CREATE TABLE `user_info` ( 9 `user_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '用户编号', 10 `user_account` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户账号', 11 `user_pw` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户密码', 12 `user_number` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户手机号', 13 `user_name` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户姓名', 14 `user_age` int(11) DEFAULT NULL COMMENT '用户年龄', 15 `user_sex` varchar(5) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户性别', 16 `user_mark` varchar(5) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户标志', 17 `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP COMMENT '用户创建时间', 18 `is_sync` int(3) DEFAULT 0 COMMENT '用户标识', 19 `is_money` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '是否缴纳押金', 20 PRIMARY KEY (`user_id`) USING BTREE 21 ) ENGINE = InnoDB AUTO_INCREMENT = 42 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '用户信息表' ROW_FORMAT = Dynamic; 22 23 SET FOREIGN_KEY_CHECKS = 1;
索引一旦进行升级优化，需要将之前废弃的索引删除掉，防止干扰。
首先进行需求查询，如下所示：
1 mysql> EXPLAIN 2 -> SELECT user_account from user_info WHERE user_age in (22,33) and user_name = '小别同志' ORDER BY user_age 3 -> ; 4 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-----------------------------+ 5 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 6 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-----------------------------+ 7 | 1 | SIMPLE | user_info | NULL | ALL | NULL | NULL | NULL | NULL | 21 | 4.76 | Using where; Using filesort | 8 +----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-----------------------------+ 9 1 row in set, 1 warning (0.00 sec) 10 11 mysql>
很明显是没有使用到索引的，那么如何才能进行优化呢。需要注意的是，需要根据sql实际解析的顺序，来调整索引的顺序。
1 编写过程：select distinct ... from ... join ... on ... where ... group by ... having ... order by ... limit ... 2 解析过程：from ... on ... join ... where ... group by ... having ... select distinct ... order by ... limit ...
如果索引顺序是这样的`user_age`, `user_name`, `user_account`，那么查询的时候是使用了索引的，符合sql的解析过程，首先是where后面的字段，然后才是select后面的字段。
1 INDEX `user_age_name_account`(`user_age`, `user_name`, `user_account`) USING BTREE
1 mysql> EXPLAIN 2 -> SELECT user_account from user_info WHERE user_age in (22,23) and user_name = '小别同志' ORDER BY user_age; 3 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 6 | 1 | SIMPLE | user_info | NULL | range | user_age_name_account | user_age_name_account | 38 | NULL | 2 | 100.00 | Using where; Using index | 7 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql>
如果是查询出所有的字段，就没有进行回表查询的，如下所示：
1 mysql> explain SELECT * from user_info WHERE user_age in (22,23) and user_name = '小别同志' ORDER BY user_age; 2 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+-----------------------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+-----------------------+ 5 | 1 | SIMPLE | user_info | NULL | range | user_age_name_account | user_age_name_account | 38 | NULL | 2 | 100.00 | Using index condition | 6 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+-----------------------+ 7 1 row in set, 1 warning (0.00 sec) 8 9 mysql>
索引一旦进行升级优化，需要将之前废弃的索引删除掉，防止干扰。
如果索引顺序是这样的`user_account`, `user_age`, `user_name`，也使用到了索引，但是进行了Using filesort，查询行数rows由2变成了21，效率下降了。
1 INDEX `user_account_age_name`(`user_account`, `user_age`, `user_name`) USING BTREE
1 mysql> EXPLAIN 2 -> SELECT user_account from user_info WHERE user_age in (22,23) and user_name = '小别同志' ORDER BY user_age; 3 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+------------------------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+------------------------------------------+ 6 | 1 | SIMPLE | user_info | NULL | index | NULL | user_account_age_name | 86 | NULL | 21 | 4.76 | Using where; Using index; Using filesort | 7 +----+-------------+-----------+------------+-------+---------------+-----------------------+---------+------+------+----------+------------------------------------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql>
索引级别type最好达到ref或者range级别的，可以再次进行优化，这里效果不明显，但是in的范围查询可能会导致索引失效，最好放到后面，如下所示：
1 mysql> EXPLAIN 2 -> SELECT user_account from user_info WHERE user_name = '小别同志' and user_age in (22,23) ORDER BY user_age; 3 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 6 | 1 | SIMPLE | user_info | NULL | range | user_age_name_account | user_age_name_account | 38 | NULL | 2 | 100.00 | Using where; Using index | 7 +----+-------------+-----------+------------+-------+-----------------------+-----------------------+---------+------+------+----------+--------------------------+ 8 1 row in set, 1 warning (0.00 sec) 9 10 mysql>
总结：mysql的索引不能跨列使用即跳过中间的索引字段（最佳左前缀），保持索引的定义和使用的顺序一致性。索引需要逐步进行优化，将含In的范围查询放到where条件的最后，防止失效，如果失效了就需要回原表进行查询了。
此案例中同时出现了Using where需要回原表查询，Using index不需要回原表查询，是因为in范围查询可能会导致索引失效就需要回原表进行查询了，如果where后面的字段在索引中就不需要回原表，可以在索引表中查询到。
1 mysql> EXPLAIN SELECT user_account from user_info WHERE user_name = '小别同志' and user_age =23 ORDER BY user_age; 2 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------------+------+----------+-------------+ 3 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 4 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------------+------+----------+-------------+ 5 | 1 | SIMPLE | user_info | NULL | ref | user_name_age_account | user_name_age_account | 38 | const,const | 1 | 100.00 | Using index | 6 +----+-------------+-----------+------------+------+-----------------------+-----------------------+---------+-------------+------+----------+-------------+ 7 1 row in set, 1 warning (0.00 sec) 8 9 mysql>
10、mysql的双表索引优化案例，如下所示：
1 SET NAMES utf8mb4; 2 SET FOREIGN_KEY_CHECKS = 0; 3 4 -- ---------------------------- 5 -- Table structure for book_info 6 -- ---------------------------- 7 DROP TABLE IF EXISTS `book_info`; 8 CREATE TABLE `book_info` ( 9 `book_id` int(11) NOT NULL COMMENT '图书编号', 10 `book_sort_id` int(11) DEFAULT NULL COMMENT '图书类型编号', 11 `book_name` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书名称', 12 `book_author` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书作者', 13 `book_price` decimal(5, 2) DEFAULT NULL COMMENT '图书价格', 14 `book_type` varchar(200) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书类型', 15 `book_publish` varchar(15) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书出版社', 16 `book_sum` int(255) DEFAULT NULL COMMENT '图书数量', 17 `book_mark` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书标识', 18 `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP COMMENT '图书创建时间', 19 `book_money` decimal(5, 2) DEFAULT NULL COMMENT '图书租金', 20 `book_desc` text CHARACTER SET utf8 COLLATE utf8_general_ci COMMENT '图书说明' 21 ) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '图书信息表' ROW_FORMAT = Dynamic; 22 23 -- ---------------------------- 24 -- Table structure for book_sort 25 -- ---------------------------- 26 DROP TABLE IF EXISTS `book_sort`; 27 CREATE TABLE `book_sort` ( 28 `book_sort_id` int(11) NOT NULL COMMENT '图书类别编号', 29 `book_sort_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书类别名称', 30 `book_sort_extend` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书类别扩展信息', 31 `book_sort_mark` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '图书类别标识', 32 `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间' 33 ) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '图书类别表' ROW_FORMAT = Dynamic; 34 35 SET FOREIGN_KEY_CHECKS = 1;
两张表组合查询，进行左外关联，如下所示：
Using join buffer (Block Nested Loop)，extra中的一个选项，作用就是mysql的引擎使用了连接缓存，其实就是你的sql太差了，mysql给你添加了一个缓存。
1 mysql> EXPLAIN 2 -> SELECT * from book_info bi LEFT OUTER JOIN book_sort bs ON bi.book_sort_id = bs.book_sort_id WHERE bi.book_name = 'Java'; 3 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+ 6 | 1 | SIMPLE | bi | NULL | ALL | NULL | NULL | NULL | NULL | 16 | 10.00 | Using where | 7 | 1 | SIMPLE | bs | NULL | ALL | NULL | NULL | NULL | NULL | 9 | 100.00 | Using where; Using join buffer (Block Nested Loop) | 8 +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+ 9 2 rows in set, 1 warning (0.01 sec) 10 11 mysql>
对于两张表的关联查询，索引向那张表加呢，这里有一个原则，叫做小表驱动大表，即where后面跟的是，小表放左边，大表放右表。索引建立到经常使用的字段上。一般情况下，对于左外连接，给左表加索引，右外连接给右表加索引。
此时可以将左表的查询字段添加上索引，增加查询速度。
1 mysql> EXPLAIN 2 -> SELECT * from book_info bi LEFT OUTER JOIN book_sort bs ON bi.book_sort_id = bs.book_sort_id WHERE bi.book_name = 'Java'; 3 +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+----------------------------------------------------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+----------------------------------------------------+ 6 | 1 | SIMPLE | bi | NULL | ref | book_name | book_name | 48 | const | 1 | 100.00 | NULL | 7 | 1 | SIMPLE | bs | NULL | ALL | NULL | NULL | NULL | NULL | 21 | 100.00 | Using where; Using join buffer (Block Nested Loop) | 8 +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+----------------------------------------------------+ 9 2 rows in set, 1 warning (0.00 sec) 10 11 mysql> 12 mysql>
如果此时右表的book_sort_id添加主键索引，此时两条都使用了索引查询，增加了查询效率，如下所示：
1 mysql> EXPLAIN 2 -> SELECT * from book_info bi LEFT OUTER JOIN book_sort bs ON bi.book_sort_id = bs.book_sort_id WHERE bi.book_name = 'Java'; 3 +----+-------------+-------+------------+--------+---------------+-----------+---------+----------------------+------+----------+-------+ 4 | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | 5 +----+-------------+-------+------------+--------+---------------+-----------+---------+----------------------+------+----------+-------+ 6 | 1 | SIMPLE | bi | NULL | ref | book_name | book_name | 48 | const | 1 | 100.00 | NULL | 7 | 1 | SIMPLE | bs | NULL | eq_ref | PRIMARY | PRIMARY | 4 | book.bi.book_sort_id | 1 | 100.00 | NULL | 8 +----+-------------+-------+------------+--------+---------------+-----------+---------+----------------------+------+----------+-------+ 9 2 rows in set, 1 warning (0.01 sec) 10 11 mysql>
11、避免mysql索引失效的一些原则。sql优化，是一种概率层面的优化，至于是否实际使用了我们的优化，需要通过explain进行推测。索引优化，是一个大部分情况适用的结论，但是由于SQL优化器等原因，该结论不是100%正确的。
1）、复合索引的时候不要跨列或者无序使用（最佳左前缀原则）。复合索引，尽量使用全索引匹配。对于复合索引，如果前面的字段索引失效，后面的字段索引就失效了。
2）、不要在索引上进行任何操作（进行计算，函数，类型转换），否则索引失效。
3）、复合索引不能使用不等于（!= 或者 <>）或者is null（is not null），否则自身以及右侧所有全部失效。复合索引中如果有>大于号，则自身和右侧索引全部失效。一般而言，范围查询>、<、in之后的索引失效。
4）、like尽量以"常量"开头，不要以'%'开头，可以将%加到常量的后面，否则索引失效。如果非要以%开头，可以使用索引覆盖，即模糊查询的字段作为查询出的字段，不用回表查询。
5）、尽量不要使用类型转换（显式转换、隐式转换），否则都会使索引失效。
6）、尽量不要使用or，否则索引失效。会将or左侧的索引失效了。
7）、对于exist和in，如果主查询的数据集大，则使用In，此时In的效率高些。如果子查询的数据集大，则使用exist，此时exist的效率高些。exist的含义就是将主查询的结果，放到子查询的结果中进行校验（看子查询是否有数据，如果有数据，则校验成功），如果复合校验，则保留数据。
8）、order by优化，using filesort有两种算法，双路排序、单路排序（根据IO的次数）。Mysql4.1之前默认使用的是双路排序，Mysql4.1之后使用的是单路排序。双路就是两次IO，会扫描两次磁盘，第一次从磁盘读取排序字段，对排序字段进行排序，第二次扫描其他字段，IO消耗性能。单路排序只读取一次，这一次就是全部的字段，在buffer中进行排序，但是单路排序，会有一定的隐患，不一定是真的一次IO，有可能是多次IO，如果数据量特别大，则无法将所有字段的数据一次性读取完毕，因此会进行分片读取。注意，单路排序会比双路排序占用更多的buffer，单路排序在使用的时候，如果数据量过大，可以考虑调大buffer的容量大小，set max_length_for_sort_data=1024，单位是字节。如果max_length_for_sort_data值太低，则mysql会自动从单路切换到双路，太低的条件是需要排序的列的总大小超过了max_length_for_sort_data定义的字节数。
总结：提高order by查询的策略，可以选择使用单路，双路，调整buffer的容量大小。避免select *的查询，只查询出需要的字段即可。复合索引，不要跨列使用，避免出现using filesort。保证全部的排序字段排序的一致性，都是升序排序或者都是降序排列。
12、mysql的慢查询日志，mysql提供的一种日志记录，用于记录mysql中响应时间超过阈值的sql语句long_query_time，默认是10秒。慢查询日志默认是关闭的，建议，在开发调优的时候打开，项目上线关闭即可。
检查是否开启了慢查询日志，如下所示：
1 mysql> show variables like '%slow_query_log%'; 2 +---------------------+-----------------------------------+ 3 | Variable_name | Value | 4 +---------------------+-----------------------------------+ 5 | slow_query_log | OFF | 6 | slow_query_log_file | /var/lib/mysql/k8s-node3-slow.log | 7 +---------------------+-----------------------------------+ 8 2 rows in set (0.00 sec) 9 10 mysql>
开启mysql的慢查询日志，临时开启，重启mysql就关闭mysql的慢查询了，在内存中开启，如下所示：
1 mysql> set global slow_query_log = 1; 2 Query OK, 0 rows affected (0.02 sec) 3 4 mysql> show variables like '%slow_query_log%'; 5 +---------------------+-----------------------------------+ 6 | Variable_name | Value | 7 +---------------------+-----------------------------------+ 8 | slow_query_log | ON | 9 | slow_query_log_file | /var/lib/mysql/k8s-node3-slow.log | 10 +---------------------+-----------------------------------+ 11 2 rows in set (0.01 sec) 12 13 mysql>
开启mysql的慢查询日志，永久开启，修改配置文件/etc/my.cnf，如下所示：
1 [mysqld] 2 slow_query_log=1 3 slow_query_log_file=/var/lib/mysql/localhost-slow.log
重启mysql，然后查看是否已经开启了慢查询，如下所示：
1 [root@k8s-node3 ~]# vim /etc/my.cnf 2 [root@k8s-node3 ~]# systemctl restart mysqld.service 3 [root@k8s-node3 ~]# mysql -uroot -h127.0.0.1 -p123456 4 mysql: [Warning] Using a password on the command line interface can be insecure. 5 Welcome to the MySQL monitor. Commands end with ; or \g. 6 Your MySQL connection id is 2 7 Server version: 5.7.30-log MySQL Community Server (GPL) 8 9 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 10 11 Oracle is a registered trademark of Oracle Corporation and/or its 12 affiliates. Other names may be trademarks of their respective 13 owners. 14 15 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 16 17 mysql> show variables like '%slow_query_log%'; 18 +---------------------+-----------------------------------+ 19 | Variable_name | Value | 20 +---------------------+-----------------------------------+ 21 | slow_query_log | ON | 22 | slow_query_log_file | /var/lib/mysql/localhost-slow.log | 23 +---------------------+-----------------------------------+ 24 2 rows in set (0.01 sec) 25 26 mysql>
查看慢查询的默认超时时间，默认超时时间是10秒钟，如下所示：
1 mysql> show variables like '%long_query_time%'; 2 +-----------------+-----------+ 3 | Variable_name | Value | 4 +-----------------+-----------+ 5 | long_query_time | 10.000000 | 6 +-----------------+-----------+ 7 1 row in set (0.00 sec) 8 9 mysql>
mysql的慢查询日志，临时超时阈值时间设置set global long_query_time = 5.000000;，需要重新登录mysql才生效，如下所示：
1 mysql> show variables like '%long_query_time%'; 2 +-----------------+-----------+ 3 | Variable_name | Value | 4 +-----------------+-----------+ 5 | long_query_time | 10.000000 | 6 +-----------------+-----------+ 7 1 row in set (0.00 sec) 8 9 mysql> set global long_query_time = 5.000000; 10 Query OK, 0 rows affected (0.00 sec) 11 12 mysql> show variables like '%long_query_time%'; 13 +-----------------+-----------+ 14 | Variable_name | Value | 15 +-----------------+-----------+ 16 | long_query_time | 10.000000 | 17 +-----------------+-----------+ 18 1 row in set (0.00 sec) 19 20 mysql> exit; 21 Bye 22 [root@k8s-node3 ~]# mysql -uroot -h127.0.0.1 -p123456 23 mysql: [Warning] Using a password on the command line interface can be insecure. 24 Welcome to the MySQL monitor. Commands end with ; or \g. 25 Your MySQL connection id is 3 26 Server version: 5.7.30-log MySQL Community Server (GPL) 27 28 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 29 30 Oracle is a registered trademark of Oracle Corporation and/or its 31 affiliates. Other names may be trademarks of their respective 32 owners. 33 34 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 35 36 mysql> show variables like '%long_query_time%'; 37 +-----------------+----------+ 38 | Variable_name | Value | 39 +-----------------+----------+ 40 | long_query_time | 5.000000 | 41 +-----------------+----------+ 42 1 row in set (0.00 sec) 43 44 mysql>
mysql的慢查询日志，永久超时阈值时间设置，需要重启mysql服务，如下所示：
1 [mysqld] 2 slow_query_log=1 3 slow_query_log_file=/var/lib/mysql/localhost-slow.log 4 long_query_time=3
重启mysql服务，如下所示：
1 [root@k8s-node3 ~]# systemctl restart mysqld.service 2 [root@k8s-node3 ~]# mysql -uroot -h127.0.0.1 -p123456 3 mysql: [Warning] Using a password on the command line interface can be insecure. 4 Welcome to the MySQL monitor. Commands end with ; or \g. 5 Your MySQL connection id is 2 6 Server version: 5.7.30-log MySQL Community Server (GPL) 7 8 Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. 9 10 Oracle is a registered trademark of Oracle Corporation and/or its 11 affiliates. Other names may be trademarks of their respective 12 owners. 13 14 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 15 16 mysql> show variables like '%long_query_time%'; 17 +-----------------+----------+ 18 | Variable_name | Value | 19 +-----------------+----------+ 20 | long_query_time | 3.000000 | 21 +-----------------+----------+ 22 1 row in set (0.00 sec) 23 24 mysql>
mysql的慢查询日志，查看慢查询的条数，如下所示：
1 mysql> select sleep(4); 2 +----------+ 3 | sleep(4) | 4 +----------+ 5 | 0 | 6 +----------+ 7 1 row in set (4.01 sec) 8 9 mysql> show global status like '%slow_queries%'; 10 +---------------+-------+ 11 | Variable_name | Value | 12 +---------------+-------+ 13 | Slow_queries | 1 | 14 +---------------+-------+ 15 1 row in set (0.00 sec) 16 17 mysql>
慢查询的sql被记录在了日志中，我们可以通过日志查看具体的慢sql，目录var/lib/mysql/localhost-slow.log是我们自己配置的，如下所示：
1 [root@k8s-node3 ~]# cat /var/lib/mysql/localhost-slow.log 2 /usr/sbin/mysqld, Version: 5.7.30-log (MySQL Community Server (GPL)). started with: 3 Tcp port: 0 Unix socket: /var/lib/mysql/mysql.sock 4 Time Id Command Argument 5 /usr/sbin/mysqld, Version: 5.7.30-log (MySQL Community Server (GPL)). started with: 6 Tcp port: 0 Unix socket: /var/lib/mysql/mysql.sock 7 Time Id Command Argument 8 # Time: 2020-07-19T13:24:44.111649Z 9 # User@Host: root[root] @ localhost [127.0.0.1] Id: 2 10 # Query_time: 4.003324 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 11 SET timestamp=1595165084; 12 select sleep(4); 13 [root@k8s-node3 ~]#
也可以通过mysqldumpslow工具查看慢sql，此是mysql自带的工具，s代表了排序方式，r代表了逆序，l代表了锁定时间，g代表了正则匹配模式，如下所示：
1 [root@k8s-node3 ~]# mysqldumpslow --help 2 Usage: mysqldumpslow [ OPTS... ] [ LOGS... ] 3 4 Parse and summarize the MySQL slow query log. Options are 5 6 --verbose verbose 7 --debug debug 8 --help write this text to standard output 9 10 -v verbose 11 -d debug 12 -s ORDER what to sort by (al, at, ar, c, l, r, t), 'at' is default 13 al: average lock time 14 ar: average rows sent 15 at: average query time 16 c: count 17 l: lock time 18 r: rows sent 19 t: query time 20 -r reverse the sort order (largest last instead of first) 21 -t NUM just show the top n queries 22 -a don't abstract all numbers to N and strings to 'S' 23 -n NUM abstract numbers with at least n digits within names 24 -g PATTERN grep: only consider stmts that include this string 25 -h HOSTNAME hostname of db server for *-slow.log filename (can be wildcard), 26 default is '*', i.e. match all 27 -i NAME name of server instance (if using mysql.server startup script) 28 -l don't subtract lock time from total time 29 30 [root@k8s-node3 ~]#
mysqldumpslow具体使用，如下所示：
1 [root@k8s-node3 ~]# mysqldumpslow -s -r -t 3 /var/lib/mysql/localhost-slow.log 2 3 Reading mysql slow query log from /var/lib/mysql/localhost-slow.log 4 Count: 6 Time=4.33s (26s) Lock=0.00s (0s) Rows=1.0 (6), root[root]@localhost 5 select sleep(N) 6 7 Died at /usr/bin/mysqldumpslow line 167, <> chunk 6. 8 [root@k8s-node3 ~]# mysqldumpslow -s -c -t 3 /var/lib/mysql/localhost-slow.log 9 10 Reading mysql slow query log from /var/lib/mysql/localhost-slow.log 11 Count: 6 Time=4.33s (26s) Lock=0.00s (0s) Rows=1.0 (6), root[root]@localhost 12 select sleep(N) 13 14 Died at /usr/bin/mysqldumpslow line 167, <> chunk 6. 15 [root@k8s-node3 ~]# mysqldumpslow -s t -t 3 "left join" /var/lib/mysql/localhost-slow.log 16 17 Reading mysql slow query log from left join /var/lib/mysql/localhost-slow.log 18 Can't open left join: No such file or directory at /usr/bin/mysqldumpslow line 97. 19 Count: 6 Time=4.33s (26s) Lock=0.00s (0s) Rows=1.0 (6), root[root]@localhost 20 select sleep(N) 21 22 Died at /usr/bin/mysqldumpslow line 167, <> chunk 6. 23 [root@k8s-node3 ~]# mysqldumpslow -s t -t 3 -g "left join" /var/lib/mysql/localhost-slow.log 24 25 Reading mysql slow query log from /var/lib/mysql/localhost-slow.log 26 Died at /usr/bin/mysqldumpslow line 167, <> chunk 6. 27 [root@k8s-node3 ~]#
13、通过profiles分析mysql的海量数据。首先创建两个数据表，如下所示：
1 SET NAMES utf8mb4; 2 SET FOREIGN_KEY_CHECKS = 0; 3 4 -- ---------------------------- 5 -- Table structure for dept 6 -- ---------------------------- 7 DROP TABLE IF EXISTS `dept`; 8 CREATE TABLE `dept` ( 9 `dno` int(11) NOT NULL, 10 `dname` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL, 11 `location` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL, 12 PRIMARY KEY (`dno`) USING BTREE 13 ) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic; 14 15 -- ---------------------------- 16 -- Table structure for emp 17 -- ---------------------------- 18 DROP TABLE IF EXISTS `emp`; 19 CREATE TABLE `emp` ( 20 `eid` int(11) NOT NULL, 21 `ename` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL, 22 `job` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL, 23 `deptno` int(5) DEFAULT NULL, 24 PRIMARY KEY (`eid`) USING BTREE 25 ) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
创建一个存储函数，方便海量插入数据，如下所示：
1 -- ---------------------------- 2 -- Function structure for randstring 3 -- ---------------------------- 4 DROP FUNCTION IF EXISTS `randstring`; 5 delimiter ;; 6 CREATE DEFINER=`root`@`localhost` FUNCTION `randstring`( n INT ) RETURNS varchar(255) CHARSET utf8 7 BEGIN 8 DECLARE 9 all_str VARCHAR ( 100 ) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; 10 DECLARE 11 return_str VARCHAR ( 255 ) DEFAULT ''; 12 DECLARE 13 i INT DEFAULT 0; 14 WHILE 15 i < n DO 16 17 SET return_str = CONCAT( return_str, SUBSTRING( all_str, FLOOR( 1 + RAND( ) * 52 ), 1 ) ); 18 19 SET i = i + 1; 20 21 END WHILE; 22 RETURN return_str; 23 24 END 25 ;; 26 delimiter ; 27 28 SET FOREIGN_KEY_CHECKS = 1; 29 30 -- 执行，如下所示： 31 32 33 mysql> delimiter $ 34 mysql> CREATE FUNCTION randstring ( n INT ) RETURNS VARCHAR ( 255 ) BEGIN 35 -> DECLARE 36 -> all_str VARCHAR ( 100 ) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; 37 -> DECLARE 38 -> return_str VARCHAR ( 255 ) DEFAULT ''; 39 -> DECLARE 40 -> i INT DEFAULT 0; 41 -> WHILE 42 -> i < n DO 43 -> 44 -> SET return_str = CONCAT( return_str, SUBSTRING( all_str, FLOOR( 1 + RAND( ) * 52 ), 1 ) ); 45 -> 46 -> SET i = i + 1; 47 -> 48 -> END WHILE; 49 -> RETURN return_str; 50 -> 51 -> END $ 52 Query OK, 0 rows affected (0.03 sec) 53 54 mysql>
创建一个生成随机数0-99的存储函数，如下所示：
1 -- 防止分号造成语义中断。 2 3 delimiter $ 4 CREATE FUNCTION rand_num ( ) RETURNS INT ( 5 ) BEGIN 5 DECLARE 6 i INT DEFAULT 0; 7 8 SET i = FLOOR( rand( ) * 100 ); 9 RETURN i; 10 11 END $
通过存储过程插入海量数据，把上面的两个存储函数使用上，注意，存储函数有返回值，存储过程没有返回值，如下所示：
1 mysql> 2 mysql> delimiter $ 3 mysql> CREATE PROCEDURE insert_emp ( IN eid_start INT ( 10 ), IN data_times INT ( 10 ) ) BEGIN 4 -> DECLARE 5 -> i INT DEFAULT 0; 6 -> 7 -> SET autocommit = 0; 8 -> REPEAT 9 -> INSERT INTO emp 10 -> VALUES 11 -> ( eid_start + i, randstring ( 5 ), 'other', rand_num ( ) ); 12 -> 13 -> SET i = i + 1; 14 -> UNTIL i = data_times 15 -> END REPEAT; 16 -> COMMIT; 17 -> 18 -> END $ 19 Query OK, 0 rows affected (0.01 sec) 20 21 mysql>
1 mysql> 2 mysql> delimiter $ 3 mysql> CREATE PROCEDURE insert_dept ( IN dno_start INT ( 10 ), IN data_times INT ( 10 ) ) BEGIN 4 -> DECLARE 5 -> i INT DEFAULT 0; 6 -> 7 -> SET autocommit = 0; 8 -> REPEAT 9 -> INSERT INTO dept 10 -> VALUES 11 -> ( dno_start + i, randstring ( 6 ), randstring ( 8 ) ); 12 -> 13 -> SET i = i + 1; 14 -> UNTIL i = data_times 15 -> END REPEAT; 16 -> COMMIT; 17 -> 18 -> END $ 19 Query OK, 0 rows affected (0.00 sec) 20 21 mysql>
编写好存储过程之后，就可以开始调用存储过程了，开始批量插入数据，如下所示：
1 mysql> delimiter ; 2 mysql> CALL insert_emp(1000,800000); 3 Query OK, 0 rows affected (1 min 8.33 sec) 4 5 mysql> 6 7 mysql> delimiter ; 8 mysql> CALL insert_dept(10,30); 9 Query OK, 0 rows affected (0.01 sec) 10 11 mysql> 12 13 mysql> select count(*) from emp; 14 +----------+ 15 | count(*) | 16 +----------+ 17 | 800000 | 18 +----------+ 19 1 row in set (0.22 sec) 20 21 mysql> select count(*) from dept; 22 +----------+ 23 | count(*) | 24 +----------+ 25 | 30 | 26 +----------+ 27 1 row in set (0.00 sec) 28 29 mysql>
海量数据已经生成了，这里通过profiles分析mysql的海量数据。 默认关闭，需要打开，如下所示：
1 mysql> show profiles; 2 Empty set, 1 warning (0.00 sec) 3 4 mysql> show variables like '%profiling%'; 5 +------------------------+-------+ 6 | Variable_name | Value | 7 +------------------------+-------+ 8 | have_profiling | YES | 9 | profiling | OFF | 10 | profiling_history_size | 15 | 11 +------------------------+-------+ 12 3 rows in set (0.04 sec) 13 14 mysql> set profiling = on; 15 Query OK, 0 rows affected, 1 warning (0.00 sec) 16 17 mysql> show variables like '%profiling%'; 18 +------------------------+-------+ 19 | Variable_name | Value | 20 +------------------------+-------+ 21 | have_profiling | YES | 22 | profiling | ON | 23 | profiling_history_size | 15 | 24 +------------------------+-------+ 25 3 rows in set (0.01 sec) 26 27 mysql> show profiles; 28 +----------+------------+-----------------------------------+ 29 | Query_ID | Duration | Query | 30 +----------+------------+-----------------------------------+ 31 | 1 | 0.00209325 | show variables like '%profiling%' | 32 +----------+------------+-----------------------------------+ 33 1 row in set, 1 warning (0.00 sec) 34 35 mysql>
show profiles会记录所有profiling打开之后的的所有sql查询语句。Query_ID是编号，Duration表示花费的时间，单位是秒，Query是查询的语句。
1 mysql> show profiles; 2 +----------+------------+-----------------------------------+ 3 | Query_ID | Duration | Query | 4 +----------+------------+-----------------------------------+ 5 | 1 | 0.00209325 | show variables like '%profiling%' | 6 +----------+------------+-----------------------------------+ 7 1 row in set, 1 warning (0.00 sec) 8 9 mysql> select count(*) from dept; 10 +----------+ 11 | count(*) | 12 +----------+ 13 | 30 | 14 +----------+ 15 1 row in set (0.00 sec) 16 17 mysql> show profiles; 18 +----------+------------+-----------------------------------+ 19 | Query_ID | Duration | Query | 20 +----------+------------+-----------------------------------+ 21 | 1 | 0.00209325 | show variables like '%profiling%' | 22 | 2 | 0.00075825 | select count(*) from dept | 23 +----------+------------+-----------------------------------+ 24 2 rows in set, 1 warning (0.00 sec) 25 26 mysql>
缺点，是Duration显示的时间不够精准，只是将cpu、IO、内存等等消费的总和。只能看到总共消费的时间，不能看到各个硬件消费的时间。
如何进行精准分析呢，需要通过一个sql诊断show profile all for query 上一步查询的Query_ID。
1 mysql> show profiles; 2 +----------+------------+-----------------------------------+ 3 | Query_ID | Duration | Query | 4 +----------+------------+-----------------------------------+ 5 | 1 | 0.00209325 | show variables like '%profiling%' | 6 | 2 | 0.00075825 | select count(*) from dept | 7 | 3 | 0.00071025 | select * from dept | 8 +----------+------------+-----------------------------------+ 9 3 rows in set, 1 warning (0.00 sec) 10 11 mysql> show profile all for query 3; 12 +----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+-----------------------+----------------------+-------------+ 13 | Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out | Messages_sent | Messages_received | Page_faults_major | Page_faults_minor | Swaps | Source_function | Source_file | Source_line | 14 +----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+-----------------------+----------------------+-------------+ 15 | starting | 0.000102 | 0.000097 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | NULL | NULL | NULL | 16 | checking permissions | 0.000017 | 0.000012 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | check_access | sql_authorization.cc | 809 | 17 | Opening tables | 0.000061 | 0.000064 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | open_tables | sql_base.cc | 5781 | 18 | init | 0.000077 | 0.000077 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | handle_query | sql_select.cc | 128 | 19 | System lock | 0.000019 | 0.000016 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | mysql_lock_tables | lock.cc | 330 | 20 | optimizing | 0.000007 | 0.000006 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | optimize | sql_optimizer.cc | 158 | 21 | statistics | 0.000054 | 0.000058 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | optimize | sql_optimizer.cc | 374 | 22 | preparing | 0.000022 | 0.000018 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | optimize | sql_optimizer.cc | 482 | 23 | executing | 0.000005 | 0.000005 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | exec | sql_executor.cc | 126 | 24 | Sending data | 0.000164 | 0.000169 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | exec | sql_executor.cc | 202 | 25 | end | 0.000013 | 0.000009 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | handle_query | sql_select.cc | 206 | 26 | query end | 0.000009 | 0.000009 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | mysql_execute_command | sql_parse.cc | 4956 | 27 | closing tables | 0.000009 | 0.000009 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | mysql_execute_command | sql_parse.cc | 5009 | 28 | freeing items | 0.000115 | 0.000118 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | mysql_parse | sql_parse.cc | 5622 | 29 | cleaning up | 0.000037 | 0.000034 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | dispatch_command | sql_parse.cc | 1931 | 30 +----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+-----------------------+----------------------+-------------+ 31 15 rows in set, 1 warning (0.01 sec) 32 33 mysql>
如果只关心部分字段，可以进行部分字段的查询，如下所示：
1 mysql> show profile cpu,block io for query 3; 2 +----------------------+----------+----------+------------+--------------+---------------+ 3 | Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out | 4 +----------------------+----------+----------+------------+--------------+---------------+ 5 | starting | 0.000102 | 0.000097 | 0.000000 | 0 | 0 | 6 | checking permissions | 0.000017 | 0.000012 | 0.000000 | 0 | 0 | 7 | Opening tables | 0.000061 | 0.000064 | 0.000000 | 0 | 0 | 8 | init | 0.000077 | 0.000077 | 0.000000 | 0 | 0 | 9 | System lock | 0.000019 | 0.000016 | 0.000000 | 0 | 0 | 10 | optimizing | 0.000007 | 0.000006 | 0.000000 | 0 | 0 | 11 | statistics | 0.000054 | 0.000058 | 0.000000 | 0 | 0 | 12 | preparing | 0.000022 | 0.000018 | 0.000000 | 0 | 0 | 13 | executing | 0.000005 | 0.000005 | 0.000000 | 0 | 0 | 14 | Sending data | 0.000164 | 0.000169 | 0.000000 | 0 | 0 | 15 | end | 0.000013 | 0.000009 | 0.000000 | 0 | 0 | 16 | query end | 0.000009 | 0.000009 | 0.000000 | 0 | 0 | 17 | closing tables | 0.000009 | 0.000009 | 0.000000 | 0 | 0 | 18 | freeing items | 0.000115 | 0.000118 | 0.000000 | 0 | 0 | 19 | cleaning up | 0.000037 | 0.000034 | 0.000000 | 0 | 0 | 20 +----------------------+----------+----------+------------+--------------+---------------+ 21 15 rows in set, 1 warning (0.00 sec) 22 23 mysql>
查看全局的查询日志（默认关闭的，需要手动开启），记录开启之后的，全部sql语句。这些全局的记录操作，仅仅在调优和开发过程中打开即可，在正式环境要进行关闭的，如下所示：
1 mysql> show variables like '%general_log%'; 2 +------------------+------------------------------+ 3 | Variable_name | Value | 4 +------------------+------------------------------+ 5 | general_log | OFF | 6 | general_log_file | /var/lib/mysql/k8s-node3.log | 7 +------------------+------------------------------+ 8 2 rows in set (0.01 sec) 9 10 mysql> set global general_log = 1; 11 Query OK, 0 rows affected (0.00 sec) 12 13 mysql> show variables like '%general_log%'; 14 +------------------+------------------------------+ 15 | Variable_name | Value | 16 +------------------+------------------------------+ 17 | general_log | ON | 18 | general_log_file | /var/lib/mysql/k8s-node3.log | 19 +------------------+------------------------------+ 20 2 rows in set (0.00 sec) 21 22 mysql>
1 mysql> set global log_output='table'; 2 Query OK, 0 rows affected (0.00 sec)
开启之后，会记录所有的sql语句的，会被记录到mysql.general_log数据表中，如下所示：
1 [root@k8s-node3 ~]# cat /var/lib/mysql/k8s-node3.log 2 /usr/sbin/mysqld, Version: 5.7.30-log (MySQL Community Server (GPL)). started with: 3 Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sock 4 Time Id Command Argument 5 2020-07-20T07:07:09.834131Z 12 Query show variables like '%general_log%' 6 2020-07-20T07:07:57.165503Z 12 Query SELECT DATABASE() 7 2020-07-20T07:07:57.166003Z 12 Init DB bigdata 8 2020-07-20T07:07:57.168232Z 12 Query show databases 9 2020-07-20T07:07:57.169327Z 12 Query show tables 10 2020-07-20T07:07:57.169786Z 12 Field List dept 11 2020-07-20T07:07:57.171001Z 12 Field List emp 12 2020-07-20T07:07:59.196072Z 12 Query show tables 13 2020-07-20T07:08:11.721455Z 12 Query select * from dept 14 2020-07-20T07:08:19.914896Z 12 Query select * from emp limit 3000 15 2020-07-20T07:08:32.237933Z 12 Query show variables like '%general_log%' 16 [root@k8s-node3 ~]#
如果开启了mysql> set global log_output='table';也可以查看mysql的数据表来查看sql语句，如下所示：
注意：这里既可以指定表也可以指定文件，看个人需求了：set global log_output='table';或者set global log_output='file';
1 mysql> select * from mysql.general_log; 2 +----------------------------+------------------------------------+-----------+-----------+--------------+---------------------------------+ 3 | event_time | user_host | thread_id | server_id | command_type | argument | 4 +----------------------------+------------------------------------+-----------+-----------+--------------+---------------------------------+ 5 | 2020-07-20 15:10:52.374558 | root[root] @ localhost [127.0.0.1] | 12 | 0 | Query | select * from mysql.general_log | 6 | 2020-07-20 15:11:27.112186 | root[root] @ localhost [127.0.0.1] | 12 | 0 | Query | select * from dept | 7 | 2020-07-20 15:11:30.430782 | root[root] @ localhost [127.0.0.1] | 12 | 0 | Query | select * from emp limit 3000 | 8 | 2020-07-20 15:11:32.430116 | root[root] @ localhost [127.0.0.1] | 12 | 0 | Query | select * from mysql.general_log | 9 +----------------------------+------------------------------------+-----------+-----------+--------------+---------------------------------+ 10 4 rows in set (0.00 sec) 11 12 mysql>
14、锁机制，解决因资源共享而造成的并发问题。锁的分类，根据操作类型分，可以分为读锁（读锁也称为共享锁）、写锁（写锁也称为互斥锁）。根据操作范围来分，可以分为表级锁、行级锁、页级锁。
1 SET NAMES utf8mb4; 2 SET FOREIGN_KEY_CHECKS = 0; 3 4 -- ---------------------------- 5 -- Table structure for user 6 -- ---------------------------- 7 DROP TABLE IF EXISTS `user`; 8 CREATE TABLE `user` ( 9 `id` int(11) NOT NULL AUTO_INCREMENT, 10 `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL, 11 PRIMARY KEY (`id`) USING BTREE 12 ) ENGINE = MyISAM AUTO_INCREMENT = 6 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic; 13 14 -- ---------------------------- 15 -- Records of user 16 -- ---------------------------- 17 INSERT INTO `user` VALUES (1, '张三'); 18 INSERT INTO `user` VALUES (2, '李四'); 19 INSERT INTO `user` VALUES (3, '王五'); 20 INSERT INTO `user` VALUES (4, '赵六'); 21 INSERT INTO `user` VALUES (5, '孙七'); 22 23 SET FOREIGN_KEY_CHECKS = 1;
14.1、根据操作类型分，可以分为读锁、写锁。
1）、读锁（共享锁）：对同一个数据，多个读操作可以同时进行，互不干扰。
2）、写锁（互斥锁）：如果当前写操作没有完毕，则无法进行其他的读操作，写操作。
14.2、根据操作范围来分，可以分为表级锁、行级锁、页级锁。
1）、表级锁：一次性对一张表整体加锁。MyISAM存储引擎（开销小，加锁快，缺点就是锁的范围大容易发生锁冲突，并发度低），是表级锁，性能优化。
2）、行级锁：一次性对一行数据进行加锁。InnoDB存储引擎（开销大，加锁慢，容易出现死锁，锁的范围较小，不易发生锁冲突，并发度高，很小的概率发生高并发问题，这些问题分别是脏读、幻读、不可重复读、丢失更新），是行级锁，事务优先，适合高并发操作。
14.3、如何查看加锁的表呢，如下所示：
1 mysql> show open tables; 2 +--------------------+------------------------------------------------------+--------+-------------+ 3 | Database | Table | In_use | Name_locked | 4 +--------------------+------------------------------------------------------+--------+-------------+ 5 | performance_schema | events_waits_summary_by_user_by_event_name | 0 | 0 | 6 | performance_schema | events_waits_summary_global_by_event_name | 0 | 0 | 7 | performance_schema | events_transactions_summary_global_by_event_name | 0 | 0 | 8 | performance_schema | replication_connection_status | 0 | 0 | 9 | performance_schema | events_waits_summary_by_account_by_event_name | 0 | 0 | 10 | mysql | engine_cost | 0 | 0 | 11 | performance_schema | metadata_locks | 0 | 0 | 12 | performance_schema | status_by_user | 0 | 0 | 13 | performance_schema | replication_group_member_stats | 0 | 0 | 14 | performance_schema | events_statements_summary_by_account_by_event_name | 0 | 0 | 15 | performance_schema | socket_summary_by_event_name | 0 | 0 | 16 | performance_schema | prepared_statements_instances | 0 | 0 | 17 | performance_schema | events_statements_history_long | 0 | 0 | 18 | performance_schema | objects_summary_global_by_type | 0 | 0 | 19 | performance_schema | file_instances | 0 | 0 | 20 | performance_schema | events_stages_summary_by_user_by_event_name | 0 | 0 | 21 | performance_schema | memory_summary_by_thread_by_event_name | 0 | 0 | 22 | performance_schema | events_stages_history_long | 0 | 0 | 23 | performance_schema | cond_instances | 0 | 0 | 24 | performance_schema | global_status | 0 | 0 | 25 | performance_schema | socket_summary_by_instance | 0 | 0 | 26 | book | user_info | 0 | 0 | 27 | performance_schema | session_status | 0 | 0 | 28 | performance_schema | session_connect_attrs | 0 | 0 | 29 | mysql | plugin | 0 | 0 | 30 | mysql | time_zone_name | 0 | 0 | 31 | performance_schema | events_statements_summary_by_program | 0 | 0 | 32 | performance_schema | events_stages_current | 0 | 0 | 33 | performance_schema | setup_instruments | 0 | 0 | 34 | book | book_sort | 0 | 0 | 35 | book | book_recommendation | 0 | 0 | 36 | mysql | func | 0 | 0 | 37 | performance_schema | events_waits_history_long | 0 | 0 | 38 | performance_schema | rwlock_instances | 0 | 0 | 39 | mysql | time_zone_leap_second | 0 | 0 | 40 | performance_schema | table_io_waits_summary_by_table | 0 | 0 | 41 | performance_schema | events_transactions_summary_by_account_by_event_name | 0 | 0 | 42 | mysql | time_zone_transition_type | 0 | 0 | 43 | performance_schema | events_waits_current | 0 | 0 | 44 | performance_schema | replication_connection_configuration | 0 | 0 | 45 | mysql | procs_priv | 0 | 0 | 46 | performance_schema | events_transactions_summary_by_user_by_event_name | 0 | 0 | 47 | performance_schema | replication_applier_configuration | 0 | 0 | 48 | performance_schema | events_statements_summary_by_user_by_event_name | 0 | 0 | 49 | performance_schema | events_stages_summary_global_by_event_name | 0 | 0 | 50 | performance_schema | replication_applier_status_by_worker | 0 | 0 | 51 | performance_schema | events_waits_summary_by_thread_by_event_name | 0 | 0 | 52 | performance_schema | session_account_connect_attrs | 0 | 0 | 53 | performance_schema | performance_timers | 0 | 0 | 54 | performance_schema | setup_consumers | 0 | 0 | 55 | performance_schema | events_statements_history | 0 | 0 | 56 | bigdata | emp | 0 | 0 | 57 | performance_schema | global_variables | 0 | 0 | 58 | mysql | gtid_executed | 0 | 0 | 59 | mysql | columns_priv | 0 | 0 | 60 | performance_schema | events_transactions_summary_by_thread_by_event_name | 0 | 0 | 61 | performance_schema | replication_applier_status_by_coordinator | 0 | 0 | 62 | mysql | db | 0 | 0 | 63 | mysql | general_log | 0 | 0 | 64 | performance_schema | events_stages_summary_by_account_by_event_name | 0 | 0 | 65 | performance_schema | variables_by_thread | 0 | 0 | 66 | book | user_book | 0 | 0 | 67 | performance_schema | events_stages_history | 0 | 0 | 68 | bigdata | dept | 0 | 0 | 69 | performance_schema | socket_instances | 0 | 0 | 70 | performance_schema | table_lock_waits_summary_by_table | 0 | 0 | 71 | mysql | time_zone | 0 | 0 | 72 | performance_schema | events_statements_summary_by_thread_by_event_name | 0 | 0 | 73 | performance_schema | users | 0 | 0 | 74 | performance_schema | setup_timers | 0 | 0 | 75 | performance_schema | memory_summary_by_host_by_event_name | 0 | 0 | 76 | performance_schema | setup_objects | 0 | 0 | 77 | performance_schema | host_cache | 0 | 0 | 78 | performance_schema | status_by_account | 0 | 0 | 79 | mysql | proxies_priv | 0 | 0 | 80 | performance_schema | memory_summary_by_account_by_event_name | 0 | 0 | 81 | performance_schema | accounts | 0 | 0 | 82 | performance_schema | replication_group_members | 0 | 0 | 83 | mysql | tables_priv | 0 | 0 | 84 | performance_schema | events_stages_summary_by_host_by_event_name | 0 | 0 | 85 | performance_schema | events_statements_current | 0 | 0 | 86 | mysql | proc | 0 | 0 | 87 | performance_schema | events_waits_summary_by_instance | 0 | 0 | 88 | performance_schema | events_statements_summary_by_host_by_event_name | 0 | 0 | 89 | performance_schema | memory_summary_by_user_by_event_name | 0 | 0 | 90 | performance_schema | events_transactions_history | 0 | 0 | 91 | mysql | event | 0 | 0 | 92 | performance_schema | status_by_host | 0 | 0 | 93 | performance_schema | setup_actors | 0 | 0 | 94 | performance_schema | threads | 0 | 0 | 95 | performance_schema | events_statements_summary_global_by_event_name | 0 | 0 | 96 | performance_schema | status_by_thread | 0 | 0 | 97 | performance_schema | file_summary_by_event_name | 0 | 0 | 98 | performance_schema | mutex_instances | 0 | 0 | 99 | performance_schema | table_handles | 0 | 0 | 100 | performance_schema | session_variables | 0 | 0 | 101 | bigdata | user | 0 | 0 | 102 | book | book_info | 0 | 0 | 103 | performance_schema | events_transactions_current | 0 | 0 | 104 | performance_schema | user_variables_by_thread | 0 | 0 | 105 | mysql | time_zone_transition | 0 | 0 | 106 | performance_schema | table_io_waits_summary_by_index_usage | 0 | 0 | 107 | performance_schema | events_transactions_history_long | 0 | 0 | 108 | performance_schema | memory_summary_global_by_event_name | 0 | 0 | 109 | performance_schema | events_statements_summary_by_digest | 0 | 0 | 110 | performance_schema | events_transactions_summary_by_host_by_event_name | 0 | 0 | 111 | performance_schema | events_waits_history | 0 | 0 | 112 | mysql | user | 0 | 0 | 113 | performance_schema | events_waits_summary_by_host_by_event_name | 0 | 0 | 114 | performance_schema | events_stages_summary_by_thread_by_event_name | 0 | 0 | 115 | performance_schema | file_summary_by_instance | 0 | 0 | 116 | mysql | server_cost | 0 | 0 | 117 | performance_schema | hosts | 0 | 0 | 118 | performance_schema | replication_applier_status | 0 | 0 | 119 | mysql | servers | 0 | 0 | 120 +--------------------+------------------------------------------------------+--------+-------------+ 121 115 rows in set (0.01 sec) 122 123 mysql>
如何加锁呢，如是，lock table 表1 read/write,表2 read/write...。首先研究的是MyISAM存储引擎的读锁，读锁（共享锁）：对同一个数据，多个读操作可以同时进行，互不干扰。
1 mysql> lock table user read; 2 Query OK, 0 rows affected (0.00 sec) 3 4 mysql> select * from user; 5 +----+--------+ 6 | id | name | 7 +----+--------+ 8 | 1 | 张三 | 9 | 2 | 李四 | 10 | 3 | 王五 | 11 | 4 | 赵六 | 12 | 5 | 孙七 | 13 +----+--------+ 14 5 rows in set (0.00 sec) 15 16 mysql>
加了读锁，是不可以进行写的（写操作就是增加、修改、删除），读就是查询。
1 mysql> delete from user where id = 1; 2 ERROR 1099 (HY000): Table 'user' was locked with a READ lock and can't be updated 3 mysql>
总结：MyISAM存储引擎，如果某一个会话，对A表加了read锁，则该会话可以对A表进行读操作，不能进行写操作，且该会话不能对其他表进行读、写操作。会话0给A表加了锁，其它会话，是可以对其他表（A表以外的表）进行读、写操作。对A表是可以读的，但是写操作的时候需要等待读锁的释放。
14.4、加写锁，会话0加写锁，如下所示：
总结：当前会话即会话0，可以对加了写锁的表进行任何操作（增删改查操作），但是不能操作（增删改查）其他表。对会话0中加写锁的表，可以进行增删改查的前提是，等待会话0释放写锁。
14.5、Mysql中表级锁的锁模式，MyISAM在执行查询语句Select前，会自动给涉及到的所有表加读锁，在执行更新操作DML前，会自动给涉及的表加写锁。所以对MyISAM表进行操作的时候会有以下情况：
a、对MyISAM表的读操作（加读锁），不会阻塞其他进程（会话）对同一表的读请求，但会阻塞对同一表的写请求。只有当读锁释放后，才会执行其他进程的写操作。
b、对MyISAM表的写操作（加写锁），会阻塞其他进程（会话）对同一表的读和写操作，只有当写锁释放后，才会执行其他进程的读写操作。
15、表锁情况分析及行锁解析，分析表锁定。
1）、查看那些表加了锁：show open tables;其中1代表加了锁。
2）、分析表锁定的严重程度：show status like 'table%';其中Table_locks_immediate表示立刻可以获取到的锁。Table_locks_waited代表了需要等待的表锁数，如果该值越大说明存在越大的锁竞争。
3）、一般建议使用Table_locks_immediate/Table_locks_waited比率来看，如果大于5000采用InnoDB引擎，如果小于5000采用MyISAM存储引擎。表锁是通过unlock tables解锁的，也可以通过事务进行解锁的，行锁是通过事务commit/rollback解锁的。
1 mysql> show open tables; 2 +--------------------+------------------------------------------------------+--------+-------------+ 3 | Database | Table | In_use | Name_locked | 4 +--------------------+------------------------------------------------------+--------+-------------+ 5 | performance_schema | events_waits_summary_by_user_by_event_name | 0 | 0 | 6 | performance_schema | events_waits_summary_global_by_event_name | 0 | 0 | 7 | performance_schema | events_transactions_summary_global_by_event_name | 0 | 0 | 8 | performance_schema | replication_connection_status | 0 | 0 | 9 | performance_schema | events_waits_summary_by_account_by_event_name | 0 | 0 | 10 | mysql | engine_cost | 0 | 0 | 11 | performance_schema | metadata_locks | 0 | 0 | 12 | performance_schema | status_by_user | 0 | 0 | 13 | performance_schema | replication_group_member_stats | 0 | 0 | 14 | performance_schema | events_statements_summary_by_account_by_event_name | 0 | 0 | 15 | performance_schema | socket_summary_by_event_name | 0 | 0 | 16 | performance_schema | prepared_statements_instances | 0 | 0 | 17 | performance_schema | events_statements_history_long | 0 | 0 | 18 | performance_schema | objects_summary_global_by_type | 0 | 0 | 19 | performance_schema | file_instances | 0 | 0 | 20 | performance_schema | events_stages_summary_by_user_by_event_name | 0 | 0 | 21 | performance_schema | memory_summary_by_thread_by_event_name | 0 | 0 | 22 | performance_schema | events_stages_history_long | 0 | 0 | 23 | performance_schema | cond_instances | 0 | 0 | 24 | performance_schema | global_status | 0 | 0 | 25 | performance_schema | socket_summary_by_instance | 0 | 0 | 26 | book | user_info | 0 | 0 | 27 | performance_schema | session_status | 0 | 0 | 28 | performance_schema | session_connect_attrs | 0 | 0 | 29 | mysql | plugin | 0 | 0 | 30 | mysql | time_zone_name | 0 | 0 | 31 | performance_schema | events_statements_summary_by_program | 0 | 0 | 32 | performance_schema | events_stages_current | 0 | 0 | 33 | performance_schema | setup_instruments | 0 | 0 | 34 | book | book_sort | 0 | 0 | 35 | book | book_recommendation | 0 | 0 | 36 | mysql | func | 0 | 0 | 37 | performance_schema | events_waits_history_long | 0 | 0 | 38 | performance_schema | rwlock_instances | 0 | 0 | 39 | mysql | time_zone_leap_second | 0 | 0 | 40 | performance_schema | table_io_waits_summary_by_table | 0 | 0 | 41 | performance_schema | events_transactions_summary_by_account_by_event_name | 0 | 0 | 42 | mysql | time_zone_transition_type | 0 | 0 | 43 | performance_schema | events_waits_current | 0 | 0 | 44 | performance_schema | replication_connection_configuration | 0 | 0 | 45 | mysql | procs_priv | 0 | 0 | 46 | performance_schema | events_transactions_summary_by_user_by_event_name | 0 | 0 | 47 | performance_schema | replication_applier_configuration | 0 | 0 | 48 | performance_schema | events_statements_summary_by_user_by_event_name | 0 | 0 | 49 | performance_schema | events_stages_summary_global_by_event_name | 0 | 0 | 50 | performance_schema | replication_applier_status_by_worker | 0 | 0 | 51 | performance_schema | events_waits_summary_by_thread_by_event_name | 0 | 0 | 52 | performance_schema | session_account_connect_attrs | 0 | 0 | 53 | performance_schema | performance_timers | 0 | 0 | 54 | performance_schema | setup_consumers | 0 | 0 | 55 | performance_schema | events_statements_history | 0 | 0 | 56 | bigdata | emp | 0 | 0 | 57 | performance_schema | global_variables | 0 | 0 | 58 | mysql | gtid_executed | 0 | 0 | 59 | mysql | columns_priv | 0 | 0 | 60 | performance_schema | events_transactions_summary_by_thread_by_event_name | 0 | 0 | 61 | performance_schema | replication_applier_status_by_coordinator | 0 | 0 | 62 | mysql | db | 0 | 0 | 63 | mysql | general_log | 0 | 0 | 64 | performance_schema | events_stages_summary_by_account_by_event_name | 0 | 0 | 65 | performance_schema | variables_by_thread | 0 | 0 | 66 | book | user_book | 0 | 0 | 67 | performance_schema | events_stages_history | 0 | 0 | 68 | bigdata | dept | 0 | 0 | 69 | performance_schema | socket_instances | 0 | 0 | 70 | performance_schema | table_lock_waits_summary_by_table | 0 | 0 | 71 | mysql | time_zone | 0 | 0 | 72 | performance_schema | events_statements_summary_by_thread_by_event_name | 0 | 0 | 73 | performance_schema | users | 0 | 0 | 74 | performance_schema | setup_timers | 0 | 0 | 75 | performance_schema | memory_summary_by_host_by_event_name | 0 | 0 | 76 | performance_schema | setup_objects | 0 | 0 | 77 | performance_schema | host_cache | 0 | 0 | 78 | performance_schema | status_by_account | 0 | 0 | 79 | mysql | proxies_priv | 0 | 0 | 80 | performance_schema | memory_summary_by_account_by_event_name | 0 | 0 | 81 | performance_schema | accounts | 0 | 0 | 82 | performance_schema | replication_group_members | 0 | 0 | 83 | mysql | tables_priv | 0 | 0 | 84 | performance_schema | events_stages_summary_by_host_by_event_name | 0 | 0 | 85 | performance_schema | events_statements_current | 0 | 0 | 86 | mysql | proc | 0 | 0 | 87 | performance_schema | events_waits_summary_by_instance | 0 | 0 | 88 | performance_schema | events_statements_summary_by_host_by_event_name | 0 | 0 | 89 | performance_schema | memory_summary_by_user_by_event_name | 0 | 0 | 90 | performance_schema | events_transactions_history | 0 | 0 | 91 | mysql | event | 0 | 0 | 92 | performance_schema | status_by_host | 0 | 0 | 93 | performance_schema | setup_actors | 0 | 0 | 94 | performance_schema | threads | 0 | 0 | 95 | performance_schema | events_statements_summary_global_by_event_name | 0 | 0 | 96 | performance_schema | status_by_thread | 0 | 0 | 97 | performance_schema | file_summary_by_event_name | 0 | 0 | 98 | performance_schema | mutex_instances | 0 | 0 | 99 | performance_schema | table_handles | 0 | 0 | 100 | performance_schema | session_variables | 0 | 0 | 101 | bigdata | user | 1 | 0 | 102 | book | book_info | 0 | 0 | 103 | performance_schema | events_transactions_current | 0 | 0 | 104 | performance_schema | user_variables_by_thread | 0 | 0 | 105 | mysql | time_zone_transition | 0 | 0 | 106 | performance_schema | table_io_waits_summary_by_index_usage | 0 | 0 | 107 | performance_schema | events_transactions_history_long | 0 | 0 | 108 | performance_schema | memory_summary_global_by_event_name | 0 | 0 | 109 | performance_schema | events_statements_summary_by_digest | 0 | 0 | 110 | performance_schema | events_transactions_summary_by_host_by_event_name | 0 | 0 | 111 | performance_schema | events_waits_history | 0 | 0 | 112 | mysql | user | 0 | 0 | 113 | performance_schema | events_waits_summary_by_host_by_event_name | 0 | 0 | 114 | mysql | slow_log | 0 | 0 | 115 | performance_schema | file_summary_by_instance | 0 | 0 | 116 | mysql | server_cost | 0 | 0 | 117 | performance_schema | hosts | 0 | 0 | 118 | performance_schema | replication_applier_status | 0 | 0 | 119 | mysql | servers | 0 | 0 | 120 | performance_schema | events_stages_summary_by_thread_by_event_name | 0 | 0 | 121 +--------------------+------------------------------------------------------+--------+-------------+ 122 116 rows in set (0.01 sec) 123 124 mysql> show status like 'table%'; 125 +----------------------------+-------+ 126 | Variable_name | Value | 127 +----------------------------+-------+ 128 | Table_locks_immediate | 411 | 129 | Table_locks_waited | 0 | 130 | Table_open_cache_hits | 3 | 131 | Table_open_cache_misses | 1 | 132 | Table_open_cache_overflows | 0 | 133 +----------------------------+-------+ 134 5 rows in set (0.01 sec) 135 136 mysql>
16、行锁的注意事项及使用情况分析：
1）、行锁的注意事项，如果没有索引，则行锁会转为表锁。如果索引列发生了类型转换，则索引失效。比如整数转换为字符串类型，导致索引失效，会导致行锁升级为表锁。
2）、行锁的一种特殊情况，间隙锁，值在范围内，但却不存在。行锁如果有where则实际加锁的范围就是where后面的范围，不是数据表中保存的实际的值。
3）、行锁的缺点比表锁性能损耗大，优点是并发能力强，效率高。InnoDB默认采用的是行锁。因此建议高并发采用InnoDB，否则使用MyISAM存储引擎。
17、行锁分析 show status like '%innodb_row_lock%';
1）、Innodb_row_lock_current_waits代表了当前正在等待锁的数量。
2）、Innodb_row_lock_time代表了等待的总时长，从系统启动到现在一共等待的时间。
3）、Innodb_row_lock_time_avg代表了平均等待时长，从系统启动到现在平均等待的时间。
4）、Innodb_row_lock_time_max代表了最大等待时长，从系统启动到现在最大一次等待的时间。
5）、Innodb_row_lock_waits代表了等待次数，从系统启动到现在一共等待的次数。
1 mysql> show status like '%innodb_row_lock%'; 2 +-------------------------------+-------+ 3 | Variable_name | Value | 4 +-------------------------------+-------+ 5 | Innodb_row_lock_current_waits | 0 | 6 | Innodb_row_lock_time | 0 | 7 | Innodb_row_lock_time_avg | 0 | 8 | Innodb_row_lock_time_max | 0 | 9 | Innodb_row_lock_waits | 0 | 10 +-------------------------------+-------+ 11 5 rows in set (0.00 sec) 12 13 mysql>
将Mysql的自动提交关闭的三种方式，第一种方式set autocommit=0;第二种方式start transaction;第三种方式begin；通过for update对query查询语句进行加锁。