MySQL-表相关sql语句
表相关sql语句
创建表
create table 表名(
字段名1 类型[(宽度) 约束条件],
字段名2 类型[(宽度) 约束条件],
字段名3 类型[(宽度) 约束条件]
);
#注意：
1. 在同一张表中，字段名是不能相同
2. 宽度和约束条件可选
3. 字段名和类型是必须的
create table staff_info
(id int,
name varchar(50),
age int(3),
sex enum('male','female'),
phone bigint(11),
job varchar(11)
);
查看表结构
describe [tablename];
desc [tablename];
效果相同；可以查看当前的表结构
查看全面的表定义信息
show create table [tablename]\G;
\G选项的含义是让记录能够竖向排列，
以便更好的显示内容较长的记录。
修改表结构
语法：alter table 表名 + 操作
修改表名
ALTER TABLE 表名 RENAME 新表名;
增加字段
ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…],
删除字段
ALTER TABLE 表名 DROP 字段名;
修改字段
ALTER TABLE 表名
MODIFY 字段名 数据类型 [完整性约束条件…];
CHANGE 旧字段名 新字段名 数据类型 [完整性约束条件…];
修改字段排列顺序
修改字段排列顺序，也可以在增加的时候指定字段位置
ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…] FIRST;
ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名;
CHANGE 字段名 旧字段名 新字段名 新数据类型 [完整性约束条件…] FIRST;
MODIFY 字段名 数据类型 [完整性约束条件…] AFTER 字段名;
sql语句操作示例：
mysql> desc staff_info;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
# 表重命名
mysql> alter table staff_info rename staff;
Query OK, 0 rows affected (0.00 sec)
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
# 删除sex列
mysql> alter table staff drop sex;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
# 添加列
mysql> alter table staff add sex enum('male','female');
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
# 修改id的宽度
mysql> alter table staff modify id int(4);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
# 修改name列的字段名
mysql> alter table staff change name sname varchar(20);
Query OK, 4 rows affected (0.03 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| sname | varchar(20) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
# 修改sex列的位置
mysql> alter table staff modify sex enum('male','female') after sname;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| sname | varchar(20) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
# 创建自增id主键
mysql> alter table staff modify id int(4) primary key auto_increment;
Query OK, 4 rows affected (0.02 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+----------------+
| id | int(4) | NO | PRI | NULL | auto_increment |
| sname | varchar(20) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
# 删除主键，可以看到删除一个自增主键会报错
mysql> alter table staff drop primary key;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
# 需要先去掉主键的自增约束，然后再删除主键约束
mysql> alter table staff modify id int(11);
Query OK, 4 rows affected (0.02 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | 0 | |
| sname | varchar(20) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | YES | | NULL | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
mysql> alter table staff drop primary key;
Query OK, 4 rows affected (0.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
# 添加联合主键
mysql> alter table staff add primary key (sname,age);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
# 删除主键
mysql> alter table staff drop primary key;
Query OK, 4 rows affected (0.02 sec)
Records: 4 Duplicates: 0 Warnings: 0
# 创建主键id
mysql> alter table staff add primary key (id);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | 0 | |
| sname | varchar(20) | NO | | | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | NO | | 0 | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
# 为主键添加自增属性
mysql> alter table staff modify id int(4) auto_increment;
Query OK, 4 rows affected (0.02 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> desc staff;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+----------------+
| id | int(4) | NO | PRI | NULL | auto_increment |
| sname | varchar(20) | NO | | | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | NO | | 0 | |
| phone | bigint(11) | YES | | NULL | |
| job | varchar(11) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
删除表
DROP TABLE 表名;
