modify与change的区别

Posted 2020-09-02 moodButterfly

 对mysql的表的表结构进行修改时，有用到change，modify两个，它们都有“改变”的意思，那它们在功能上有什么区别了？做个试验比较下

 

1、字段重命名：

1）change

mysql> alter table t1 change number id char(2);

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

 

2）modify

mysql> alter table t1 modify id num int(2);

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘num int(2)‘ at line 1

mysql>

结论：能用change重命名，而modify不能。

 

2、修改字段类型和约束

1）modify

mysql> alter table t1 modify id int(2);

Query OK, 0 rows affected (0.06 sec)

Records: 0  Duplicates: 0  Warnings: 0

 

mysql> alter table t1 modify id int(2) not null;

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

 

2）change

 

mysql> alter table t1 change id char(2);

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘char(2)‘ at line 1

 

 

mysql> alter table t1 change id char(2) not null;

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘char(2) not null‘ at line 1

 

结论：modify能修改字段类型和约束，而change不能。

 

最终结论：change用来字段重命名，不能修改字段类型和约束；

         modify不用来字段重命名，只能修改字段类型和约束；