對mysql的表的表結構進行修改時，有用到change，modify兩個，它們都有“改變”的意思，那它們在功能上有什么區別了？做個試驗比較下
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>
結論：能用change重命名，而modify不能。
2、修改字段類型和約束
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
結論：modify能修改字段類型和約束，而change不能。
最終結論：change用來字段重命名，不能修改字段類型和約束；
modify不用來字段重命名，只能修改字段類型和約束；