Mysql DDL常见操作汇总

库的管理

创建库

create database [if not exists] 库名;

drop databases [if exists] 库名;

drop database if exists 旧库名;create database 新库名;

mysql> show databases like 'javacode2018';+-------------------------+| Database (javacode2018) |+-------------------------+| javacode2018      |+-------------------------+1 row in set (0.00 sec)mysql> drop database if exists javacode2018;Query OK, 0 rows affected (0.00 sec)mysql> show databases like 'javacode2018';Empty set (0.00 sec)mysql> create database javacode2018;Query OK, 1 row affected (0.00 sec)

表管理

创建表

create table 表名(  字段名1 类型[(宽度)] [约束条件] [comment '字段说明'],  字段名2 类型[(宽度)] [约束条件] [comment '字段说明'],  字段名3 类型[(宽度)] [约束条件] [comment '字段说明'])[表的一些设置];

在同一张表中，字段名不能相同
宽度和约束条件为可选参数，字段名和类型是必须的
最后一个字段后不能加逗号
类型是用来限制字段必须以何种数据类型来存储记录
类型其实也是对字段的约束(约束字段下的记录必须为XX类型)
类型后写的约束条件是在类型之外的额外添加的约束

约束说明

not null：标识该字段不能为空

mysql> create table test1(a int not null comment '字段a');Query OK, 0 rows affected (0.01 sec)mysql> insert into test1 values (null);ERROR 1048 (23000): Column 'a' cannot be nullmysql> insert into test1 values (1);Query OK, 1 row affected (0.00 sec)mysql> select * from test1;+---+| a |+---+| 1 |+---+1 row in set (0.00 sec)

mysql> drop table IF EXISTS test2;Query OK, 0 rows affected (0.01 sec)mysql> create table test2(  ->  a int not null comment '字段a',  ->  b int not null default 0 comment '字段b'  -> );Query OK, 0 rows affected (0.02 sec)mysql> insert into test2(a) values (1);Query OK, 1 row affected (0.00 sec)mysql> select *from test2;+---+---+| a | b |+---+---+| 1 | 0 |+---+---+1 row in set (0.00 sec)

**primary key：**标识该字段为该表的主键，可以唯一的标识记录，插入重复的会报错

两种写法，如下：

方式1：跟在列后，如下：

mysql> drop table IF EXISTS test3;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql> create table test3(  ->  a int not null comment '字段a' primary key  -> );Query OK, 0 rows affected (0.01 sec)mysql> insert into test3 (a) values (1);Query OK, 1 row affected (0.01 sec)mysql> insert into test3 (a) values (1);ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'

mysql> drop table IF EXISTS test4;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql> create table test4(  ->  a int not null comment '字段a',  ->  b int not null default 0 comment '字段b',  ->  primary key(a)  -> );Query OK, 0 rows affected (0.02 sec)mysql> insert into test4(a,b) values (1,1);Query OK, 1 row affected (0.00 sec)mysql> insert into test4(a,b) values (1,2);ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'

方式2支持多字段作为主键，多个之间用逗号隔开，语法：primary key(字段1,字段2,字段n)，示例：

mysql> drop table IF EXISTS test7;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test7(  ->  a int not null comment '字段a',  ->  b int not null comment '字段b',  ->  PRIMARY KEY (a,b)  -> );Query OK, 0 rows affected (0.02 sec)mysql>mysql> insert into test7(a,b) VALUES (1,1);Query OK, 1 row affected (0.00 sec)mysql> insert into test7(a,b) VALUES (1,1);ERROR 1062 (23000): Duplicate entry '1-1' for key 'PRIMARY'

语法：foreign key(当前表的列名) references 引用的外键表(外键表中字段名称)

mysql> drop table IF EXISTS test6;Query OK, 0 rows affected (0.01 sec)mysql> drop table IF EXISTS test5;Query OK, 0 rows affected (0.01 sec)mysql>mysql> create table test5(  ->  a int not null comment '字段a' primary key  -> );Query OK, 0 rows affected (0.02 sec)mysql>mysql> create table test6(  ->  b int not null comment '字段b',  ->  ts5_a int not null,  ->  foreign key(ts5_a) references test5(a)  -> );Query OK, 0 rows affected (0.01 sec)mysql> insert into test5 (a) values (1);Query OK, 1 row affected (0.00 sec)mysql> insert into test6 (b,test6.ts5_a) values (1,1);Query OK, 1 row affected (0.00 sec)mysql> insert into test6 (b,test6.ts5_a) values (2,2);ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`javacode2018`.`test6`, CONSTRAINT `test6_ibfk_1` FOREIGN KEY (`ts5_a`) REFERENCES `test5` (`a`))

注意几点：

两张表中需要建立外键关系的字段类型需要一致
要设置外键的字段不能为主键
被引用的字段需要为主键
被插入的值在外键表必须存在，如上面向test6中插入ts5_a为2的时候报错了，原因：2的值在test5表中不存在

unique key(uq)：标识该字段的值是唯一的

支持一个到多个字段，插入重复的值会报违反唯一约束，会插入失败。

定义有2种方式。

方式1：跟在字段后，如下：

mysql> drop table IF EXISTS test8;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test8(  ->  a int not null comment '字段a' unique key  -> );Query OK, 0 rows affected (0.01 sec)mysql>mysql> insert into test8(a) VALUES (1);Query OK, 1 row affected (0.00 sec)mysql> insert into test8(a) VALUES (1);ERROR 1062 (23000): Duplicate entry '1' for key 'a'

mysql> drop table IF EXISTS test9;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test9(  ->  a int not null comment '字段a',  ->  unique key(a)  -> );Query OK, 0 rows affected (0.01 sec)mysql>mysql> insert into test9(a) VALUES (1);Query OK, 1 row affected (0.00 sec)mysql> insert into test9(a) VALUES (1);ERROR 1062 (23000): Duplicate entry '1' for key 'a'

mysql> drop table IF EXISTS test10;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test10(  ->  a int not null comment '字段a',  ->  b int not null comment '字段b',  ->  unique key(a,b)  -> );Query OK, 0 rows affected (0.01 sec)mysql>mysql> insert into test10(a,b) VALUES (1,1);Query OK, 1 row affected (0.00 sec)mysql> insert into test10(a,b) VALUES (1,1);ERROR 1062 (23000): Duplicate entry '1-1' for key 'a'

mysql> drop table IF EXISTS test11;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test11(  ->  a int not null AUTO_INCREMENT PRIMARY KEY comment '字段a',  ->  b int not null comment '字段b'  -> );Query OK, 0 rows affected (0.01 sec)mysql>mysql> insert into test11(b) VALUES (10);Query OK, 1 row affected (0.00 sec)mysql> insert into test11(b) VALUES (20);Query OK, 1 row affected (0.00 sec)mysql> select * from test11;+---+----+| a | b |+---+----+| 1 | 10 || 2 | 20 |+---+----+2 rows in set (0.00 sec)

关于自动增长字段的初始值、步长可以在mysql中进行设置，比如设置初始值为1万，每次增长10

注意：
自增长列当前值存储在内存中，数据库每次重启之后，会查询当前表中自增列的最大值作为当前值，如果表数据被清空之后，数据库重启了，自增列的值将从初始值开始

我们来演示一下：

mysql> delete from test11;Query OK, 2 rows affected (0.00 sec)mysql> insert into test11(b) VALUES (10);Query OK, 1 row affected (0.00 sec)mysql> select * from test11;+---+----+| a | b |+---+----+| 3 | 10 |+---+----+1 row in set (0.00 sec)

删除test11数据，重启mysql，插入数据，然后看a的值是不是被初始化了？如下：

mysql> delete from test11;Query OK, 1 row affected (0.00 sec)mysql> select * from test11;Empty set (0.00 sec)mysql> exitByeC:\Windows\system32>net stop mysqlmysql 服务正在停止..mysql 服务已成功停止。C:\Windows\system32>net start mysqlmysql 服务正在启动 .mysql 服务已经启动成功。C:\Windows\system32>mysql -uroot -pEnter password: *******Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 2Server version: 5.7.25-log MySQL Community Server (GPL)Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> use javacode2018;Database changedmysql> select * from test11;Empty set (0.01 sec)mysql> insert into test11 (b) value (100);Query OK, 1 row affected (0.00 sec)mysql> select * from test11;+---+-----+| a | b  |+---+-----+| 1 | 100 |+---+-----+1 row in set (0.00 sec)

drop table [if exists] 表名;

alter table 表名 rename [to] 新表名;

alter table 表名 comment '备注信息';

create table 表名 like 被复制的表名;

mysql> create table test12 like test11;Query OK, 0 rows affected (0.01 sec)mysql> select * from test12;Empty set (0.00 sec)mysql> show create table test12;+--------+-------+| Table | Create Table                                                                      +--------+-------+| test12 | CREATE TABLE `test12` ( `a` int(11) NOT NULL AUTO_INCREMENT COMMENT '字段a', `b` int(11) NOT NULL COMMENT '字段b', PRIMARY KEY (`a`)) ENGINE=InnoDB DEFAULT CHARSET=utf8   |+--------+-------+1 row in set (0.00 sec)

create table 表名 [as] select 字段,... from 被复制的表 [where 条件];

mysql> create table test13 as select * from test11;Query OK, 1 row affected (0.02 sec)Records: 1 Duplicates: 0 Warnings: 0mysql> select * from test13;+---+-----+| a | b  |+---+-----+| 1 | 100 |+---+-----+1 row in set (0.00 sec)

表中列的管理

添加列

alter table 表名 add column 列名 类型 [列约束];

mysql> drop table IF EXISTS test14;Query OK, 0 rows affected, 1 warning (0.00 sec)mysql>mysql> create table test14(  ->  a int not null AUTO_INCREMENT PRIMARY KEY comment '字段a'  -> );Query OK, 0 rows affected (0.02 sec)mysql> alter table test14 add column b int not null default 0 comment '字段b';Query OK, 0 rows affected (0.03 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> alter table test14 add column c int not null default 0 comment '字段c';Query OK, 0 rows affected (0.05 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> insert into test14(b) values (10);Query OK, 1 row affected (0.00 sec)mysql> select * from test14;                         c+---+----+---+| a | b | c |+---+----+---+| 1 | 10 | 0 |+---+----+---+1 row in set (0.00 sec)

alter table 表名 modify column 列名 新类型 [约束];或者alter table 表名 change column 列名 新列名 新类型 [约束];

我们看一下test14的表结构：

mysql> show create table test14;+--------+--------+| Table | Create Table |+--------+--------+| test14 | CREATE TABLE `test14` ( `a` int(11) NOT NULL AUTO_INCREMENT COMMENT '字段a', `b` int(11) NOT NULL DEFAULT '0' COMMENT '字段b', `c` int(11) NOT NULL DEFAULT '0' COMMENT '字段c', PRIMARY KEY (`a`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8    |+--------+--------+1 row in set (0.00 sec)

mysql> alter table test14 change column c d varchar(10) not null default '' comment '字段d';Query OK, 0 rows affected (0.01 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> show create table test14;                             ;;+--------+--------+| Table | Create Table |+--------+--------+| test14 | CREATE TABLE `test14` ( `a` int(11) NOT NULL AUTO_INCREMENT COMMENT '字段a', `b` int(11) NOT NULL DEFAULT '0' COMMENT '字段b', `d` varchar(10) NOT NULL DEFAULT '' COMMENT '字段d', PRIMARY KEY (`a`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8    |+--------+--------+1 row in set (0.00 sec)

alter table 表名 drop column 列名;

mysql> alter table test14 drop column d;Query OK, 0 rows affected (0.05 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> show create table test14;+--------+--------+| Table | Create Table |+--------+--------+| test14 | CREATE TABLE `test14` ( `a` int(11) NOT NULL AUTO_INCREMENT COMMENT '字段a', `b` int(11) NOT NULL DEFAULT '0' COMMENT '字段b', PRIMARY KEY (`a`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8   |+--------+--------+1 row in set (0.00 sec)

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