数据结构模型主要有:
关系模型:
二维关系:row,column
数据库管理系统:DBMS
关系:Relational,RDBMS
SQL:Structure Query Language,结构化查询语言
SQL 约束:constraint,用于限制加入表的数据的类型。
索引:将表中的一个或多个字段中的数据复制一份另存,并且这些数据需要按特定次序排序存储
关系型数据库的常见组件有:
SQL语句有三种类型:
SQL语句类型 | 对应操作 |
---|---|
DDL | CREATE:创建 DROP:删除 ALTER:修改 |
DML | INSERT:向表中插入数据 DELETE:删除表中数据 UPDATE:更新表中数据 SELECT:查询表中数据 |
DCL | GRANT:授权 REVOKE:移除授权 |
由于MySQL和MariaDB是同一个开发团队制作的软件,所以操作方式差不多,而且MariaDB是免费的,这里就用MariaDB作为演示。
[root@localhost ~]# yum -y install mariadb*
//设置mariadb开机自动启动
[root@localhost ~]# systemctl enable --now mariadb
//确保3306端口已经监听起来
[root@localhost ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 100 127.0.0.1:25 *:*
LISTEN 0 50 *:3306 *:*
LISTEN 0 128 *:22 *:*
LISTEN 0 100 [::1]:25 [::]:*
LISTEN 0 128 [::]:22 [::]:*
//登录mariadb
[root@localhost ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> //看到有这样的标识符则表示成功登录了
//设置mariadb登录密码
MariaDB [(none)]> set password = password('12321');
Query OK, 0 rows affected (0.00 sec)
//修改密码后登录
[root@localhost ~]# mysql -uroot -p12321
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
//语法:mysql [OPTIONS] [database]
//常用的OPTIONS:
-uUSERNAME //指定用户名,默认为root
-hHOST //指定服务器主机,默认为localhost,推荐使用ip地址
-pPASSWORD //指定用户的密码
-P# //指定数据库监听的端口,这里的#需用实际的端口号代替,如-P3307
-V //查看当前使用的mysql版本
-e //不登录mysql执行sql语句后退出,常用于脚本
//查看版本信息
[root@localhost ~]# mysql -V
mysql Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1
//指定服务器主机(必须先授权才能连接)
//如:客户机IP:192.168.118.133 服务器IP:192.168.118.134
//服务器操作:
[root@localhost ~]# mysql -uroot -p12321
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 4
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> grant all on *.* to 'root'@192.168.118.133 identified by '12321';Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
//现在客户机可以连接服务器了:
[root@localhost ~]# mysql -uroot -p12321 -h192.168.118.134
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 5
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
//使用交互式输入密码
[root@localhost ~]# mysql -u root -p
Enter password: //输入密码
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 8
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
//不登录mysql执行sql语句
[root@localhost ~]# mysql -uroot -p12321 -e'show databases;'
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
ip socket:默认监听在tcp的3306端口,支持远程通信
unix sock
//通过sock文件连接
[root@localhost ~]# mysql -uroot -p12321 -S /var/lib/mysql/mysql.sock
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 14
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
//创建数据库
//语法:CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';
//创建数据库school
MariaDB [(none)]> create database if not exists school;
Query OK, 1 row affected (0.00 sec)
//查看当前实例有哪些数据库
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| test |
+--------------------+
5 rows in set (0.00 sec)
//删除数据库
//语法:DROP DATABASE [IF EXISTS] 'DB_NAME';
//删除数据库school
MariaDB [(none)]> drop database if exists school;
Query OK, 0 rows affected, 1 warning (0.00 sec)
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set (0.01 sec)
//创建表
//语法:CREATE TABLE table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型';
//在数据库school里创建表20200520
MariaDB [(none)]> create database school; //创建数据库school
Query OK, 1 row affected (0.00 sec)
MariaDB [(none)]> use school; //进入school数据库
Database changed
MariaDB [school]> create table Linux0520(id int not null,name varchar(50) not null,age tinyint not null);
Query OK, 0 rows affected (0.01 sec)
//查看当前数据库有哪些表
MariaDB [school]> show tables;
+------------------+
| Tables_in_school |
+------------------+
| Linux0520 |
+------------------+
1 row in set (0.00 sec)
//删除表
//语法:DROP TABLE [ IF EXISTS ] 'table_name';
//删除表school
MariaDB [school]> drop table Linux0520;
Query OK, 0 rows affected (0.00 sec)
MariaDB [school]> show tables;
Empty set (0.00 sec)
mysql用户帐号由两部分组成,如’USERNAME’@‘HOST’,表示此USERNAME只能从此HOST上远程登录
这里(‘USERNAME’@‘HOST’)的HOST用于限制此用户可通过哪些主机远程连接mysql程序,其值可为:
//数据库用户创建
//语法:CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];
//创建数据库用户tom
MariaDB [(none)]> create user 'tom'@'127.0.0.1' identified by '12321';
Query OK, 0 rows affected (0.05 sec)
//使用新创建的用户和密码登录
[root@localhost ~]# mysql -utom -p12321 -h127.0.0.1
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
//删除数据库用户
//语法:DROP USER 'username'@'host';
MariaDB [(none)]> drop user 'tom'@'127.0.0.1';
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> show character set;
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
......
......
//第一种方法
MariaDB [(none)]> show engines;
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Percona-XtraDB, Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MyISAM | YES | Non-transactional engine with good performance and small data footprint | NO | NO | NO |
......
......
//第二种方法
MariaDB [(none)]> show engines\G
*************************** 1. row ***************************
Engine: InnoDB
Support: DEFAULT
Comment: Percona-XtraDB, Supports transactions, row-level locking, and foreign keys
Transactions: YES
XA: YES
Savepoints: YES
*************************** 2. row ***************************
Engine: MRG_MYISAM
Support: YES
Comment: Collection of identical MyISAM tables
Transactions: NO
XA: NO
Savepoints: NO
......
......
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| test |
+--------------------+
5 rows in set (0.07 sec)
MariaDB [(none)]> show tables from school;
+------------------+
| Tables_in_school |
+------------------+
| Linux0520 |
+------------------+
1 row in set (0.00 sec)
MariaDB [(none)]> show create table school.Linux0520;
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
| Linux0520 | CREATE TABLE `Linux0520` (
`id` int(11) NOT NULL,
`name` varchar(50) NOT NULL,
`age` tinyint(4) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [school]> use school; //进入数据库school
Database changed
MariaDB [school]> show table status like 'Linux0520'\G
*************************** 1. row ***************************
Name: Linux0520
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 10485760
Auto_increment: NULL
Create_time: 2020-05-21 02:17:42
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
MariaDB [(none)]> desc school.Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | NO | | NULL | |
| age | tinyint(4) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
//获取命令使用帮助
//语法:HELP keyword;
MariaDB [(none)]> help create table; //获取创建表的帮助
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
(create_definition,...)
[table_options]
[partition_options]
Or:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
[(create_definition,...)]
[table_options]
[partition_options]
select_statement
......
......
DML操作包括增(INSERT)、删(DELETE)、改(UPDATE)、查(SELECT),均属针对表的操作。
//DML操作之增操作insert
//语法:INSERT [INTO] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...
MariaDB [(none)]> use school;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
MariaDB [school]> insert into Linux0520 (id,name,age) value (1,'tom',20);
Query OK, 1 row affected (0.00 sec)
MariaDB [school]> insert into Linux0520 (id,name,age) values (2,'jerry',23),(3,'jack',18),(4,'zhangsan',25),(5,'lisi',26),(6,'wangwu',NULL);
Query OK, 5 rows affected, 1 warning (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 1
字段column表示法
表示符 | 代表什么? |
---|---|
* | 所有字段 |
as | 字段别名,如col1 AS alias1 当表名很长时用别名代替 |
条件判断语句WHERE
操作类型 | 常用操作符 |
---|---|
操作符 | >,<,>=,<=,=,!= BETWEEN column# AND column# LIKE:模糊匹配 RLIKE:基于正则表达式进行模式匹配 IS NOT NULL:非空 IS NULL:空 |
条件逻辑操作 | AND OR NOT |
ORDER BY:排序,默认为升序(ASC)
ORDER BY语句 | 意义 |
---|---|
ORDER BY ‘column_name’ | 根据column_name进行升序排序 |
ORDER BY ‘column_name’ DESC | 根据column_name进行降序排序 |
ORDER BY ’column_name’ LIMIT 2 | 根据column_name进行升序排序 并只取前2个结果 |
ORDER BY ‘column_name’ LIMIT 1,2 | 根据column_name进行升序排序 并且略过第1个结果取后面的2个结果 |
//DML操作之查操作select
//语法:SELECT column1,column2,... FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
MariaDB [school]> select * from Linux0520
-> ;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> select id as 学生编号,name from Linux0520;
+--------------+----------+
| 学生编号 | name |
+--------------+----------+
| 1 | tom |
| 2 | jerry |
| 3 | jack |
| 4 | zhangsan |
| 5 | lisi |
| 6 | wangwu |
+--------------+----------+
6 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age is not null order by age;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 6 | wangwu | 0 |
| 3 | jack | 18 |
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 order by age desc;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 5 | lisi | 26 |
| 4 | zhangsan | 25 |
| 2 | jerry | 23 |
| 1 | tom | 20 |
| 3 | jack | 18 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 order by age limit 2;
+----+--------+-----+
| id | name | age |
+----+--------+-----+
| 6 | wangwu | 0 |
| 3 | jack | 18 |
+----+--------+-----+
2 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 order by age limit 1,2;
+----+------+-----+
| id | name | age |
+----+------+-----+
| 3 | jack | 18 |
| 1 | tom | 20 |
+----+------+-----+
2 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 order by age limit 1;
+----+--------+-----+
| id | name | age |
+----+--------+-----+
| 6 | wangwu | 0 |
+----+--------+-----+
1 row in set (0.00 sec)
MariaDB [school]> select * from Linux0520 order by age desc limit 1;
+----+------+-----+
| id | name | age |
+----+------+-----+
| 5 | lisi | 26 |
+----+------+-----+
1 row in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age > 20;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 2 | jerry | 23 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
+----+----------+-----+
3 rows in set (0.01 sec)
MariaDB [school]> select * from Linux0520 where age > 20 and name = 'zhangsan';
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 4 | zhangsan | 25 |
+----+----------+-----+
1 row in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age between 23 and 26;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 2 | jerry | 23 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
+----+----------+-----+
3 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age is not null;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age = 23 or name = 'lisi';
+----+-------+-----+
| id | name | age |
+----+-------+-----+
| 2 | jerry | 23 |
| 5 | lisi | 26 |
+----+-------+-----+
2 rows in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where age like '2%';
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
+----+----------+-----+
4 rows in set (0.01 sec)
MariaDB [school]> select * from Linux0520 where age rlike '1[0-9]'; //查询年龄是1开头的
+----+------+-----+
| id | name | age |
+----+------+-----+
| 3 | jack | 18 |
+----+------+-----+
1 row in set (0.00 sec)
MariaDB [school]> select * from Linux0520 where name rlike '^[a-z]{3}$'; //查名字是3个字母的
+----+------+-----+
| id | name | age |
+----+------+-----+
| 1 | tom | 20 |
+----+------+-----+
1 row in set (0.00 sec)
GROUP BY:分组,用于结合聚合函数,根据一个或多个列对结果集进行分组
//语法:SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;
//表websites的数据
MariaDB [RUNOOB]> use RUNOOB;
Database changed
MariaDB [RUNOOB]> select * from websites;
+----+--------------+---------------------------+-------+---------+
| id | name | url | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA |
| 2 | 淘宝 | https://www.taobao.com/ | 13 | CN |
| 3 | 菜鸟教程 | http://www.runoob.com/ | 4689 | CN |
| 4 | 微博 | http://weibo.com/ | 20 | CN |
| 5 | Facebook | https://www.facebook.com/ | 3 | USA |
+----+--------------+---------------------------+-------+---------+
5 rows in set (0.00 sec)
//表access_log的数据
MariaDB [RUNOOB]> select * from access_log;
+-----+---------+-------+------------+
| aid | site_id | count | date |
+-----+---------+-------+------------+
| 1 | 1 | 45 | 2016-05-10 |
| 2 | 3 | 100 | 2016-05-13 |
| 3 | 1 | 230 | 2016-05-14 |
| 4 | 2 | 10 | 2016-05-14 |
| 5 | 5 | 205 | 2016-05-14 |
| 6 | 4 | 13 | 2016-05-15 |
| 7 | 3 | 220 | 2016-05-15 |
| 8 | 5 | 545 | 2016-05-16 |
| 9 | 3 | 201 | 2016-05-17 |
+-----+---------+-------+------------+
9 rows in set (0.00 sec)
MariaDB [RUNOOB]> select site_id, sum(access_log.count) as num from access_log group by site_id;
+---------+------+
| site_id | num |
+---------+------+
| 1 | 275 |
| 2 | 10 |
| 3 | 521 |
| 4 | 13 |
| 5 | 750 |
+---------+------+
5 rows in set (0.00 sec)
MariaDB [RUNOOB]> select websites.name,count(access_log.aid) as nums from access_log left join websites on access_log.site_id=websites.id group by websites.name;
+--------------+------+
| name | nums |
+--------------+------+
| Facebook | 2 |
| Google | 2 |
| 微博 | 1 |
| 淘宝 | 1 |
| 菜鸟教程 | 3 |
+--------------+------+
5 rows in set (0.00 sec)
//DML操作之改操作update
//语法:UPDATE table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> update Linux0520 set age = 30 where name = 'lisi'; //将lisi的年龄修改为30岁
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [school]> select * from Linux0520 where name = 'lisi';
+----+------+-----+
| id | name | age |
+----+------+-----+
| 5 | lisi | 30 |
+----+------+-----+
1 row in set (0.00 sec)
//DML操作之删操作delete
//语法:DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 30 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> delete from Linux0520 where id = 6;
Query OK, 1 row affected (0.00 sec)
MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 30 |
+----+----------+-----+
5 rows in set (0.00 sec)
MariaDB [school]> delete from Linux0520;
Query OK, 5 rows affected (0.00 sec)
MariaDB [school]> select * from Linux0520;
Empty set (0.00 sec)
MariaDB [school]> desc Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | NO | | NULL | |
| age | tinyint(4) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.06 sec)
truncate与delete的区别:
语句类型 | 特点 |
---|---|
delete |
DELETE删除表内容时仅删除内容,但会保留表结构 DELETE语句每次删除一行,并在事务日志中为所删除的每行记录一项 可以通过回滚事务日志恢复数据 非常占用空间 |
truncate |
删除表中所有数据,且无法恢复 表结构、约束和索引等保持不变,新添加的行计数值重置为初始值 执行速度比DELETE快,且使用的系统和事务日志资源少 通过释放存储表数据所用的数据页来删除数据,并且只在事务日志中记录页的释放 对于有外键约束引用的表,不能使用TRUNCATE TABLE删除数据 不能用于加入了索引视图的表 |
//语法:TRUNCATE table_name;
MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name | age |
+----+----------+-----+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | jack | 18 |
| 4 | zhangsan | 25 |
| 5 | lisi | 26 |
| 6 | wangwu | 0 |
+----+----------+-----+
6 rows in set (0.00 sec)
MariaDB [school]> truncate Linux0520;
Query OK, 0 rows affected (0.00 sec)
MariaDB [school]> select * from Linux0520;
Empty set (0.00 sec)
MariaDB [school]> desc Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | NO | | NULL | |
| age | tinyint(4) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
权限类型(priv_type)
权限类型 | 代表什么? |
---|---|
ALL | 所有权限 |
SELECT | 读取内容的权限 |
INSERT | 插入内容的权限 |
UPDATE | 更新内容的权限 |
DELETE | 删除内容的权限 |
指定要操作的对象db_name.table_name
表示方式 | 意义 |
---|---|
*.* | 所有库的所有表 |
db_name | 指定库的所有表 |
db_name.table_name | 指定库的指定表 |
WITH GRANT OPTION:被授权的用户可将自己的权限副本转赠给其他用户,说白点就是将自己的权限完全复制给另一个用户。不建议使用。
//语法:GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| test |
+--------------------+
5 rows in set (0.05 sec)
//授权tom用户在数据库本机上登录访问所有数据库
MariaDB [(none)]> grant all on *.* to 'tom'@'localhost' identified by '12321';
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> grant all on *.* to 'tom'@'127.0.0.1' identified by '12321';
Query OK, 0 rows affected (0.00 sec)
//授权tom用户在192.168.118.133上远程登录访问school数据库
MariaDB [(none)]> grant all on school.* to 'tom'@'192.168.118.133' identified by '12321';
Query OK, 0 rows affected (0.00 sec)
//授权tom用户在所有位置上远程登录访问school数据库
MariaDB [(none)]> grant all on *.* to 'tom'@'%' identified by '12321';
Query OK, 0 rows affected (0.00 sec)
//授权tom用户school数据库的Linux0520表的插入权限
MariaDB [school]> grant insert on school.Linux0520 to 'tom'@'localhost' identified by '12321';
Query OK, 0 rows affected (0.00 sec)
MariaDB [school]> show grants;
+----------------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost |
+----------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION |
+----------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
MariaDB [school]> show grants for tom;
+-------------------------------------------------------------------------------------------------------------+
| Grants for tom@% |
+-------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'%' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' |
+-------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [school]> show grants for 'tom'@'localhost';
+---------------------------------------------------------------------------------------------------------------------+
| Grants for tom@localhost |
+---------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'localhost' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' |
| GRANT INSERT ON `school`.`Linux0520` TO 'tom'@'localhost' |
+---------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
//语法:REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';
MariaDB [school]> revoke all on *.* from 'tom'@'localhost';
Query OK, 0 rows affected (0.00 sec)
MariaDB [school]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
注意:mysql服务进程启动时会读取mysql库中的所有授权表至内存中:
mysql> FLUSH PRIVILEGES;
//mysql -uroot -p 输入密码回车后,出现如下图错误。这时候需要我们破解密码。
[root@localhost ~]# mysql -uroot -p'hello'
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root@localhost ~]# systemctl stop mariadb
[root@localhost ~]# vim /etc/my.cnf
[mysqld]
skip-grant-tables //添加该行代码开机跳过授权表
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
......
......
[root@localhost ~]# systemctl restart mariadb
[root@localhost ~]# mysql -uroot -p
Enter password: //直接回车
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> //成功进入数据库
MariaDB [(none)]> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
MariaDB [mysql]> update user set password=password('123456') where user="root"; //更改密码
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4 Changed: 4 Warnings: 0
MariaDB [mysql]> quit
Bye
[root@localhost ~]# vim /etc/my.cnf //删除skip-grant-tables
[root@localhost ~]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
......
......
[root@localhost ~]# systemctl restart mariadb
[root@localhost ~]# mysql -uroot -p'123456'
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> //成功连接说明密码破解成功
[root@localhost ~]# yum -y install mariadb*
[root@localhost ~]# systemctl enable --now mariadb
Created symlink from /etc/systemd/system/multi-user.target.wants/mariadb.service to /usr/lib/systemd/system/mariadb.service.
[root@localhost ~]# ss -antl | grep 3306
LISTEN 0 50 *:3306 *:*
[root@localhost ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> set password = password('123456'); //设置mysql密码
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> quit
Bye
[root@localhost ~]# mysql -uroot -p123456 //用密码登录mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)
MariaDB [(none)]> create database linux;
Query OK, 1 row affected (0.00 sec)
MariaDB [(none)]> use linux;
Database changed
MariaDB [linux]> create table student(id int primary key auto_increment not null,name varchar(100) not null,age tinyint(4));
Query OK, 0 rows affected (0.01 sec)
MariaDB [linux]> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
MariaDB [linux]> select * from student;
Empty set (0.00 sec)
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | NULL |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
MariaDB [linux]> insert into student(name,age) values('tom',20),('jerry',23),('wangqing',25),('sean',28),('zhangshan',26),('zhangshan',20);
Query OK, 6 rows affected (0.00 sec)
Records: 6 Duplicates: 0 Warnings: 0
MariaDB [linux]> insert into student(name) value('lisi');
Query OK, 1 row affected (0.00 sec)
MariaDB [linux]> insert into student(name,age) values('chenshuo',10),('wangwu',3),('qiuyi',15),('qiuxiaotian',20);
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
MariaDB [linux]> select * from student;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | NULL |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
11 rows in set (0.00 sec)
MariaDB [linux]> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [linux]> select * from student where name = 'lisi';
+----+------+------+
| id | name | age |
+----+------+------+
| 7 | lisi | 50 |
+----+------+------+
1 row in set (0.00 sec)
MariaDB [linux]> select * from student order by age desc;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
| 2 | jerry | 23 |
| 1 | tom | 20 |
| 6 | zhangshan | 20 |
| 11 | qiuxiaotian | 20 |
| 10 | qiuyi | 15 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
+----+-------------+------+
11 rows in set (0.00 sec)
MariaDB [linux]> select * from student order by age limit 2,3;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 10 | qiuyi | 15 |
| 1 | tom | 20 |
| 6 | zhangshan | 20 |
+----+-----------+------+
3 rows in set (0.00 sec)
MariaDB [linux]> select * from student order by age desc limit 4;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
+----+-----------+------+
4 rows in set (0.00 sec)
MariaDB [linux]> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
+----+-----------+------+
2 rows in set (0.00 sec)
MariaDB [linux]> select * from student where name = 'zhangshan' and age > 20;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 5 | zhangshan | 26 |
+----+-----------+------+
1 row in set (0.00 sec)
MariaDB [linux]> select * from student where age between 20 and 30;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
7 rows in set (0.00 sec)
MariaDB [linux]> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [linux]> select * from student where name = 'wangwu';
+----+--------+------+
| id | name | age |
+----+--------+------+
| 9 | wangwu | 100 |
+----+--------+------+
1 row in set (0.00 sec)
MariaDB [linux]> delete from student where name = 'zhangshan' and age <= 20;
Query OK, 1 row affected (0.00 sec)
MariaDB [linux]> select * from student;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 7 | lisi | 50 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 100 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
10 rows in set (0.00 sec)