MYSQL结构修改

Posted 2021-05-07 眼界、格局、胸怀

mysql改表结构主要是5大操作

ADD 　　添加字段

MODIFY 修改字段类型

CHANGE 修改字段名(也可以修改字段名)

DROP 　　删除字段

RENAME 修改表名

 

ADD添加新字段:(新字段默认添加在所有字段末尾,可以设定位置)

语法结构为:

　　ALTER TABLE 库名.表名

　　ADD 列名 类型(范围) 约束条件

　　[ AFTER 字段名 | FRIST ]

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
10 rows in set (0.00 sec)

例如我在fri_name后添加一个fri_from

mysql> ALTER TABLE f_fri_list
　　 -> ADD fri_from CHAR(30)
　　 -> AFTER fri_name;

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_from | char(30) | YES | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
11 rows in set (0.00 sec)

如果是要在列首添加一个行叫fri_ot

mysql> ALTER TABLE f_fri_list
　　 -> ADD fri_ot char(100)
　　 -> first;

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| fri_ot | char(100) | YES | | NULL | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_from | char(30) | YES | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
12 rows in set (0.00 sec)

MODIFY修改字段类型(修改的字段类型不能与已存储的数据冲突)

语法结构为

　　ALTER TABLE 库名.表名

　　MODIFY 列名 类型(范围) 约束条件

　　[ AFTER 字段名 | FRIST ]

除了关键字变成了MODIFY之外其他与ADD一致

例如我需要将fri_ot 类型改成 varchar类型(限定范围为200) 并放到最后一列去则

mysql> ALTER TABLE f_fri_list
　　 -> MODIFY fri_ot varchar(100)
　　 -> AFTER create_time;

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_from | char(30) | YES | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
| fri_ot | varchar(100) | YES | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
12 rows in set (0.00 sec)

CHANGE 修改字段名(也可以用来修改字段类型)

　　ALTER TABLE 库名.表名

　　CHANGE 源列名 新列名 类型(范围) 约束条件

例如 我需要将fri_ot 列名改为 fri_ot2

mysql> ALTER TABLE f_fri_list
　 -> CHANGE fri_ot fri_ot2 varchar(100);

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_from | char(30) | YES | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
| fri_ot2 | varchar(100) | YES | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
12 rows in set (0.00 sec)

删除字段(表中有记录时,所有记录中此字段的值都会被删除)

　　ALTER TABLE 库名.表名

　　DROP 列名

例如要删除fri_ot2字段

mysql> ALTER TABLE f_fri_list
　　 -> DROP fri_ot2;

mysql> DESC f_fri_list;
+---------------+-------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| type | enum(‘男‘,‘女‘) | NO | | NULL | |
| fri_id | int(10) unsigned | NO | | NULL | |
| fri_name | char(10) | NO | | NULL | |
| fri_from | char(30) | YES | | NULL | |
| fri_phone_num | char(11) | YES | | NULL | |
| fri_email | varchar(20) | YES | | NULL | |
| fri_wecat | varchar(20) | YES | | NULL | |
| fri_brithday | date | YES | | NULL | |
| create_date | date | NO | | NULL | |
| create_time | time | NO | | NULL | |
+---------------+-------------------+------+-----+---------+----------------+
11 rows in set (0.00 sec)

修改表名(表对应的文件名,也被改变)

　　ALTER TABLE 表名

　　RENAME 新表名

例如将f_fri_list 改成 fri_list

mysql> ALTER TABLE f_fri_list
　　 -> RENAME fri_list;

mysql> SHOW TABLES;
+--------------------+
| Tables_in_f_friend |
+--------------------+
| f_fri_type |
| fri_list |
+--------------------+
2 rows in set (0.00 sec)