MySQL第二课（库的操作、表的操作、数据类型）
库操作&表操作：
mysql>
create database a;
//创建数据库a
Query OK, 1 row affected (0.00 sec)
mysql>
show create database a;
+----------+--------------------------------------------------------------+
| Database | Create Database |
+----------+--------------------------------------------------------------+
| a | CREATE DATABASE `a` /*!40100 DEFAULT CHARACTER SET latin1 */ |
//latin1是当前使用的字符编码格式
+----------+--------------------------------------------------------------+
1 row in set (0.00 sec
mysql>
show charset;
//显示字符编码
……
mysql>
help create database;
//获取create database的帮助
……
mysql>
create database b default charset=utf8;
//创建数据库b，并指定（更改）默认字符编码为utf8
mysql>
show create database b;
//显示创建数据库b的信息
+----------+------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------+
| b | CREATE DATABASE `b` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+------------------------------------------------------------+
mysql>
create table if not exists student (name varchar(32));
//创建student表
Query OK, 0 rows affected (0.03 sec)
mysql>
insert into student values ('a'),('A'),('b'),('B');
//写入四条数据
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql>
select * from student;
//显示表中数据
+------+
| name |
+------+
| a |
| A |
| b |
| B |
+------+
4 rows in set (0.00 sec)
mysql>
select * from student where name ='a';
//默认的校验规则不分大小写，所以a和A都显示
+------+
| name |
+------+
| a |
| A |
+------+
2 rows in set (0.00 sec)
show collation;
//显示校验规则
mysql>
create database if not exists c default charset=utf8 collate utf8_bin;
//创建数据库c，默认编码为utf8，默认校验规则为
collate utf8_bin
Query OK, 1 row affected (0.00 sec)
mysql>
show create database c;
//显示？……
+----------+-----------------------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------------------+
| c | CREATE DATABASE `c` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */ |
+----------+-----------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql>
use c;
Database changed
mysql>
create table if not exists student (name varchar(32));
//创建student表
Query OK, 0 rows affected (0.01 sec)
mysql>
insert into student values ('a'),('A'),('b'),('B');
//写入数据
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql>
select * from student where name='a';
//utf8_bin区分大小写，所以只有a
+------+
| name |
+------+
| a |
+------+
1 row in set (0.00 sec)
mysql>
select * from student order by name;
//依据名字排序 校验规则也会影响排序
+------+
| name |
+------+
| A |
| B |
| a |
| b |
+------+
4 rows in set (0.00 sec)
校验规则的影响：
（1）大小写 （不区分大小写：邮箱、windows创建文件夹的名字； 区分大小写：密码、linux系统下的文件名）
（2）排序
mysql>
exit
//退出数据库
Bye
[du@localhost ~]$
which mysql
//查看mysql所在位置
/usr/bin/mysql
[du@localhost ~]$
ls /usr/bin/mysql*
/usr/bin/mysql /usr/bin/mysql_fix_privilege_tables
/usr/bin/mysqlaccess /usr/bin/mysqlhotcopy
/usr/bin/mysqladmin /usr/bin/mysqlimport
/usr/bin/mysqlbinlog /usr/bin/mysql_install_db
/usr/bin/mysqlbug /usr/bin/mysql_secure_installation
/usr/bin/mysqlcheck /usr/bin/mysql_setpermission
/usr/bin/mysql_config /usr/bin/mysqlshow
/usr/bin/mysql_convert_table_format /usr/bin/mysqlslap
/usr/bin/mysqld_multi /usr/bin/mysqltest
/usr/bin/mysqld_safe /usr/bin/mysql_tzinfo_to_sql
/usr/bin/mysqldump /usr/bin/mysql_upgrade
/usr/bin/mysqldumpslow /usr/bin/mysql_waitpid
/usr/bin/mysql_find_rows /usr/bin/mysql_zap
/usr/bin/mysql_fix_extensions
[du@localhost ~]$
mysqldump //备份命令
Usage: mysqldump [OPTIONS] database [tables]
OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]
OR mysqldump [OPTIONS] --all-databases [OPTIONS]
For more options, use mysqldump --help
[du@localhost ~]$
mysqldump -u root -p --databases c > /c_db.sql
//备份数据库c （重定义>为/c_db.sql)
bash: /c_db.sql: Permission denied
//转到root用户下再执行
[du@localhost ~]$
su - root
[root@localhost ~]#
mysqldump -u root -p --databases b > /c_db.sql
//备份数据库c到/c_db.sql
Enter password:
[root@localhost ~]#
mysql -u root -p
//再次连接数据库
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.1.73 Source distribution
Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
drop database b;
//前面已经备份成功，这里可以删除数据库b
Query OK, 1 row affected (0.00 sec)
mysql>
show databases;
/
/显示当前存在的数据库，已经没有了数据库b
+--------------------+
| Database |
+--------------------+
| information_schema |
| a |
| c |
| mysql |
| test |
+--------------------+
5 rows in set (0.00 sec)
mysql>
source /c_db.sql
//恢复/c_db.sql ？？？
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 1 row affected (0.00 sec)
Database changed
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 8 rows affected (0.00 sec)
Records: 8 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
mysql>
show databases;
//恢复成功，再来显示当前存在的数据库，数据库b又回来了
+--------------------+
| Database |
+--------------------+
| information_schema |
| a |
| b |
| c |
| mysql |
| test |
+--------------------+
6 rows in set (0.00 sec)
mysql>
show columns from student;
//显示表结构（显示每一列）
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name | varchar(32) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql>
show processlist;
//查看当前连接的人
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+------------------+
//只有一个id为11的连接者
| 11 | root | localhost | b | Query | 0 | NULL | show processlist |
+----+------+-----------+------+---------+------+-------+------------------+
1 row in set (0.00 sec)
mysql>
kill 11;
//删掉id为11的连接者
Query OK, 0 rows affected (0.00 sec)
mysql>
show processlist;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
//因为只有一个还删了，所以重新分配并连接
Connection id: 12
Current database: b
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+------------------+
| 12 | root | localhost | b | Query | 0 | NULL | show processlist |
+----+------+-----------+------+---------+------+-------+------------------+
1 row in set (0.00 sec)
一个实例（包括库的操作和表的操作）：
mysql>
create database if not exists bit default character set utf8 collate utf8_general_ci;
//没有简写 character set=charset
Query OK, 1 row affected (0.00 sec)
mysql>
show create database bit;
+----------+--------------------------------------------------------------+
| Database | Create Database |
+----------+--------------------------------------------------------------+
| bit | CREATE DATABASE `bit` /*!40100 DEFAULT CHARACTER SET utf8 */ |
//不显示校验规则是因为默认的校验规则就是utf8_general_ci
+----------+--------------------------------------------------------------+
1 row in set (0.00 sec)
mysql>
alter table user add column login varchar(32);
//给user表加一列login
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql>
desc user;
//显示user的属性设置
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| login | varchar(32) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql>
insert into user values (1,'bit',md5('123'),'123');
//给user表添加一条信息（采用加密密码）
Query OK, 1 row affected (0.00 sec)
mysql>
select * from user;
//显示user表中的所有数据
+------+------+----------------------------------+-------+
| id | name | password | login |
+------+------+----------------------------------+-------+
| 1 | bit | 202cb962ac59075b964b07152d234b70 | 123 |
+------+------+----------------------------------+-------+
1 row in set (0.00 sec)
mysql>
alter table user modify column name varchar(8);
//修改user表中name的属性（varchar(32)->varchar(8)）
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql>
desc user;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(8) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| login | varchar(32) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql>
alter table user modify column name varchar(1);
//修改user表中name的属性（varchar(8)->varchar(1)）
Query OK, 1 row affected, 1 warning (0.01 sec)
//虽然有一条警告，但修改成功
Records: 1 Duplicates: 0 Warnings: 1
mysql>
desc user;
//没有报错 数据库中有信息长于1个字符却没有报错，不正常
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(1) | YES | | NULL | |
//name已被修改为varchar(1)
| password | varchar(32) | YES | | NULL | |
| login | varchar(32) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql>
select * from user;
+------+------+----------------------------------+-------+
| id | name | password | login |
+------+------+----------------------------------+-------+
| 1 | b | 202cb962ac59075b964b07152d234b70 | 123 |
//name=bit被截成name=b
+------+------+----------------------------------+-------+
1 row in set (0.00 sec)
mysql>
set sql_mode=strict_trans_tables;
//严格校验，报错 之前不报错是因为版本低 >5.7.4版本的时候才能开启
Query OK, 0 rows affected (0.00 sec)
mysql>
alter table user modify column password varchar(1);
//再修改password为varchar(1)时报错,因为表中已经有md5加密后的密码“123”，长度大于1个字符
ERROR 1265 (01000): Data truncated for column 'password' at row 1
mysql>
alter table user drop column name;
//删除user表的name列
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql>
desc user;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| login | varchar(32) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql>
drop table if exists user;
//删除user表
Query OK, 0 rows affected (0.00 sec)
mysql>
show tables;
Empty set (0.00 sec)
mysql>
drop table user;
//再删报错（不加if exists）
ERROR 1051 (42S02): Unknown table 'user'
mysql>
drop table if exists user;
Query OK, 0 rows affected, 1 warning (0.00 sec)
//警告（加上if exists）
mysql>
show warnings;
//查看警告
+-------+------+----------------------+
| Level | Code | Message |
+-------+------+----------------------+
| Note | 1051 | Unknown table 'user' |
+-------+------+----------------------+
1 row in set (0.00 sec)
mysql>
create table user (id int , name varchar(32), login varchar(32), password varchar(32));
//重建user表
Query OK, 0 rows affected (0.01 sec)
mysql>
alter table user change column name nick varchar(32);
//修改name列的名字为nick
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql>
desc user;
//显示表的属性设置 修改成功
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
//default即默认 表示默认值
| id | int(11) | YES | | NULL | |
| nick | varchar(32) | YES | | NULL | |
| login | varchar(32) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
数据类型：
mysql>
help data types;
//出错
Nothing found
Please try to run 'help contents' for a list of all accessible topics
mysql>
help contents;
//要先获取目录，再翻到具体的章节
……
mysql>
help data types;
//再获取data types的帮助
mysql>
create table t1 (a int , b bit(8));
//创建t1表 a为int类型，b为bit类型
Query OK, 0 rows affected (0.01 sec)
mysql>
insert into t1 values(10,10);
//给a 10，给b也是10
Query OK, 1 row affected (0.00 sec)
mysql>
select * from t1;
+------+------+
| a | b |
+------+------+
//10是一个不可见的字符（ASSII码）
| 10 |
|
+------+------+
1 row in set (0.00 sec)
mysql>
insert into t1 values(10,65);
//65对应字符A
Query OK, 1 row affected (0.00 sec)
mysql>
select * from t1;
+------+------+
| a | b |
+------+------+
| 10 |
|
| 10 | A |
+------+------+
2 rows in set (0.00 sec)
mysql>
create table t2 (name bit(65));
//bit类型的最大值为64位
ERROR 1439 (42000): Display width out of range for column 'name' (max = 64)
mysql>
create table t3 (a int unsigned , b int unsigned);
//设置为无符号int型
Query OK, 0 rows affected (0.01 sec)
mysql>
insert into t3 value (1,1);
//插入一条数据 a=1，b=1
Query OK, 1 row affected (0.00 sec)
mysql>
select * from t3;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
mysql>
select a-b from t3;
//查询a-b的值
+------+
| a-b |
+------+
| 0 |
+------+
1 row in set (0.00 sec)
mysql>
insert into t3 value (1,2);
Query OK, 1 row affected (0.00 sec)
mysql>
select * from t3;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
| 1 | 2 |
+------+------+
2 rows in set (0.00 sec)
mysql>
select a-b from t3;
//无符号数类型下，1-2！=-1
+----------------------+
| a-b |
+----------------------+
| 0 |
| 18446744073709551615 |
+----------------------+
2 rows in set (0.00 sec)
mysql>
set sql_mode=no_unsigned_subtraction;
//为了得到想要的结果，用该命令更改设置
Query OK, 0 rows affected (0.00 sec)
mysql>
select * from t3;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
| 1 | 2 |
+------+------+
2 rows in set (0.00 sec)
mysql>
select a-b from t3;
//得到-1
+------+
| a-b |
+------+
| 0 |
| -1 |
+------+
2 rows in set (0.00 sec)
mysql>
insert into t1 values (300,300);
Query OK, 1 row affected, 1 warning (0.00 sec)
//给出警告 但成功 不应该成功，应该报错
mysql>
show warnings;
+---------+------+--------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------+
//越界
| Warning | 1264 | Out of range value for column 'b' at row 1 |
+---------+------+--------------------------------------------+
1 row in set (0.00 sec
mysql>
set sql_mode=strict_trans_tables;
//防止越界，严格校验，报错
Query OK, 0 rows affected (0.00 sec)
mysql>
select * from t1;
+------+------+
| a | b |
+------+------+
| 10 |
|
| 10 | A |
| 300 | � |
//乱码
+------+------+
3 rows in set (0.00 sec)
mysql>
insert into t1 values (300,300);
ERROR 1406 (22001): Data too long for column 'b' at row 1
//设置后插入300大小的bit类型，会报错