mysql 表的增删改查 修改表结构
四、修改表结构
语法: 1. 修改表名 ALTER TABLE 表名 RENAME 新表名; 2. 增加字段 ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…], ADD 字段名 数据类型 [完整性约束条件…]; ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…] FIRST; ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名; 3. 删除字段 ALTER TABLE 表名 DROP 字段名; 4. 修改字段 ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…]; ALTER TABLE 表名 CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…]; ALTER TABLE 表名 CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];
1. 修改表名
ALTER TABLE 表名
RENAME 新表名;
修改表名 rename
mysql> create table t2(id int,name char(5)); Query OK, 0 rows affected (0.24 sec) mysql> show tables; +---------------+ | Tables_in_db1 | +---------------+ | innodb__t_t1 | | innodb__t_t2 | | innodb__t_t3 | | innodb__t_t4 | | t1 | | t2 | +---------------+ 6 rows in set (0.00 sec) mysql> alter table t2 rename t3; Query OK, 0 rows affected (0.20 sec) mysql> show tables; +---------------+ | Tables_in_db1 | +---------------+ | innodb__t_t1 | | innodb__t_t2 | | innodb__t_t3 | | innodb__t_t4 | | t1 | | t3 | +---------------+ 6 rows in set (0.00 sec)
2. 增加字段
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…],
ADD 字段名 数据类型 [完整性约束条件…];
添加字段
mysql> alter table t3 add age int,add sex enum('male','female'); Query OK, 0 rows affected (0.21 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(5) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.10 sec)
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…] FIRST;
指定添加的字段在哪个位置
first 添加到第一个
mysql> alter table t3 add hobby char(50) first; Query OK, 0 rows affected (0.17 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | hobby | char(50) | YES | | NULL | | | id | int(11) | YES | | NULL | | | name | char(5) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 5 rows in set (0.00 sec)
放在哪个字段的后面
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名;
mysql> alter table t3 add hobby char(50) after name; Query OK, 0 rows affected (0.09 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(5) | YES | | NULL | | | hobby | char(50) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 5 rows in set (0.01 sec)
3. 删除字段
ALTER TABLE 表名
DROP 字段名;
mysql> alter table t3 drop hobby ; Query OK, 0 rows affected (0.06 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(5) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec)
4. 修改字段
ALTER TABLE 表名
MODIFY 字段名 数据类型 [完整性约束条件…]
mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(5) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> alter table t3 modify name char(11) ; Query OK, 0 rows affected (0.92 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(11) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.04 sec)
改数据类型
mysql> alter table t3 modify name int(11) ; Query OK, 0 rows affected (0.20 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | int(11) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec)
ALTER TABLE 表名
CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…];
mysql> alter table t3 change name NAME int(11) ; Query OK, 0 rows affected (0.06 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | NAME | int(11) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec)
ALTER TABLE 表名
CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];
mysql> alter table t3 change NAME name char(11) ; Query OK, 0 rows affected (0.25 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(11) | YES | | NULL | | | age | int(11) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.04 sec)
总结:
如果只想改数据类型 用modify
如果想改字段名 或者 想改 字段名 和数据类型 用change