mysql基础操作

1.创建数据库：

　　create database dbname

　　例：　　

mysql> create database test1;
Query OK, 1 row affected (0.00 sec)

2.查看有哪些数据库：

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
| test1 |
+--------------------+
5 rows in set (0.01 sec)

• information_schema：主要存储了系统中的一些数据库对象信息，比如用户表信息、列信息、权限信息、字符集信息、分区信息等。
• mysql：存储了系统的用户权限信息。
• test：系统自动创建的测试数据库，任何用户不都可以使用。

3.进入数据库：

mysql> use test1;
Database changed

4.查看数据库中的表：　

mysql> show tables;
+---------------------------+
| Tables_in_mysql |
+---------------------------+
| columns_priv |
| db |
| event |
| func |
| general_log |

5.删除数据库：

　　drop database dbname;

　　例：

mysql> drop database test1;
Query OK, 0 rows affected (0.00 sec)

6.创建表

　　create table tablename (

　　column_name_1 column_type_1 constraints,

　　column_name_2 column_type_2 constraints,

　　.....

　　column_name_n column_type_n constraints)

　　例：

mysql> create table emp(
-> ename varchar(10),
-> hiredate date,
-> sal decimal(10,2),
-> deptno int(2));
Query OK, 0 rows affected (0.02 sec)

7.查看表的定义

　　desc tablename

　　例：

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.查看创建表语句

mysql> show create table empG;
*************************** 1. row ***************************
Table: emp
Create Table: CREATE TABLE `emp` (
`ename` varchar(10) DEFAULT NULL,
`hiredate` date DEFAULT NULL,
`sal` decimal(10,2) DEFAULT NULL,
`deptno` int(2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

ERROR:
No query specified

 9.删除表

　　drop table tablename

　　例：

mysql> drop table ca1;
Query OK, 0 rows affected (0.00 sec)

 10.修改表

　　1.修改表类型：

　　　　alter table tablename modify[column] column_definition[first|after col_name]

　　　　例：

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)

mysql> alter table emp modify ename varchar(20);
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(20) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

　　2.增加表字段

　　　　alter table tablename add [column]column_definition[first|after col_name]

　　　　例：

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(20) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> alter table emp add column age int(3);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(20) | 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)

　　3.删除表字段

　　　　alter table tablename drop [column]col_name

　　　　例：

mysql> alter table emp drop column age;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

4.字段改名

　　alter table tablename change[column] old_col_name column_definition [first|after col_name]

　　例 ：

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(20) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno | int(2) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

mysql> alter table emp change deptno deptno1 int(4);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(20) | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno1 | int(4) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

　　　　注意：

　　　　　　change和modify都可以修改表的定义，不同的是chenge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。

　　5.修改字段排列顺序

　　　　将字段增加在某字段之后

mysql> alter table emp add birth date after ename;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename | varchar(20) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno1 | int(4) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

将字段增加在最前面

mysql> alter table emp add age int(6) first;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| age | int(6) | YES | | NULL | |
| ename | varchar(20) | YES | | NULL | |
| birth | date | YES | | NULL | |
| hiredate | date | YES | | NULL | |
| sal | decimal(10,2) | YES | | NULL | |
| deptno1 | int(4) | YES | | NULL | |
+----------+---------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

　　6.更改表名

　　　　alter table tablename rename [to] new_tablename

　　　　例：

mysql> alter table emp rename emp1;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| emp1 |
+-----------------+
1 row in set (0.00 sec)