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  • modify与change的区别

     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;

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  • 原文地址:https://www.cnblogs.com/mood-butterfly/p/6509472.html
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