DDL语句（DDL：数据定义语言）
1.创建数据库：create database test1;
2.显示数据库：show databases;
3.选择数据库：use mysql;
4.查询数据库所有的表：show tables;
5.删除数据库：drop database test1;
6.创建表：create table emp(ename varchar(10),hiredate date,sal decimal(10,2),deptno int(2));
7.查看表结构：
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(10) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
8.查看创建表的SQL语句：
mysql> show create table emp \G;
*************************** 1. row ***************************
Table: emp
Create Table: CREATE TABLE `emp` (
`ename` varchar(10) COLLATE utf8_unicode_ci DEFAULT NULL,
`hiredate` date DEFAULT NULL,
`sal` decimal(10,2) DEFAULT NULL,
`deptno` int(2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
1 row in set (0.02 sec)
9.删除表：drop table emp;
10.修改表：
修改表的类型
修改表emp的ename字段定义，将varchar(10)修改为varchar(50)
mysql> alter table emp modify ename varchar(50);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(50) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
增加表字段
在表emp中增加字段age,类型为int(3)
mysql> alter table emp add column age int(3);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(50) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
删除表字段：
删除字段age
mysql> alter table emp drop column age;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(50) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
字段改名：
将字段age改名为age1,同时修改字段类型为int(4)
mysql> alter table emp change age age1 int(4);
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(50) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
| age1 | int(4) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
注：change 和 modify都可以修改表的定义，不同的是change后面需要写两次列名，不方便，但是change的优点是可以修改列名称，modify则不能。
修改字段排列顺序：
字段增加和修改语法（ADD/CHANGE/MODIFY）中，都有一个可选项first|after column_name,这个选项可以修改字段在表中的位置，ADD增加的新字段默认是加在表的最后位置，而CHANGE/MODIFY默认都不会改变字段的位置。
增加字段birth date到ename后
mysql> alter table emp add birth date after ename;
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(50) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
| age1 | int(4) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
修改字段age1为age,并放到最前面
mysql> alter table emp change age1 age int(3) first;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| age | int(3) | YES | | NULL | |
| ename | varchar(50) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
注：CHANGE/FIRST|AFTER COLUMN这些关键字都属于MYSQL的标准SQL上的扩展，在其他数据库不一定适用。
更改表名：
将emp表修改为为emp1
mysql> alter table emp rename emp1;
Query OK, 0 rows affected (0.00 sec)
mysql> desc emp;
ERROR 1146 (42S02): Table ‘test1.emp‘ doesn‘t exist
mysql> desc emp1;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| age | int(3) | YES | | NULL | |
| ename | varchar(50) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
原文地址：http://csy520.blog.51cto.com/2896920/1626740
