Mysql DDL常见操作汇总

Mysql DDL常见操作汇总

库的管理

创建库

create database [if not exists] 库名;

删除库

drop databases [if exists] 库名;

建库通用的写法

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

示例

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)

 

show databases like ‘javacode2018";列出javacode2018库信息。

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];

注意:

  • 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 null
mysql> 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)

**default value:**为该字段设置默认值,默认值为value

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)

上面插入时未设置b的值,自动取默认值0

**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"

方式2:在所有列定义之后定义,如下:

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"

插入重复的值,会报违法主键约束

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"

foreign key:为表中的字段设置外键

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`))

说明:表示test6中ts5_a字段的值来源于表test5中的字段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"

方式2:所有列定义之后定义,如下:

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"

方式2支持多字段,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 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"

auto_increment:标识该字段的值自动增长(整数类型,而且为主键)

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)

字段a为自动增长,默认值从1开始,每次+1

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)

上面删除了test11数据,然后插入了一条,a的值为3,执行下面操作:

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> exit
Bye

C:Windowssystem32>net stop mysql
mysql 服务正在停止..
mysql 服务已成功停止。


C:Windowssystem32>net start mysql
mysql 服务正在启动 .
mysql 服务已经启动成功。


C:Windowssystem32>mysql -uroot -p
Enter password: *******
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 2
Server 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 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> use javacode2018;
Database changed
mysql> 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)

删除表

drop table [if exists] 表名;

修改表名

alter table 表名 rename [to] 新表名;

表设置备注

alter table 表名 comment "备注信息";

复制表

create table 表名 like 被复制的表名;

如:

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)

复制表结构+数据

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

如:

mysql> create table test13 as select * from test11;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from test13;
+---+-----+
| a | b  |
+---+-----+
| 1 | 100 |
+---+-----+
1 row in set (0.00 sec)

表结构和数据都过来了。

表中列的管理

添加列

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

示例:

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: 0

mysql> 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: 0

mysql> 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)

修改列

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];

2种方式区别:modify不能修改列名,change可以修改列名

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)

我们将字段c名字及类型修改一下,如下:

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: 0

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",
 `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)

删除列

alter table 表名 drop column 列名;

示例:

mysql> alter table test14 drop column d;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

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",
 PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8   |
+--------+--------+
1 row in set (0.00 sec)

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原文链接:https://blog.csdn.net/m0_47157676/article/details/108514295