SQL 如何改变约束
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How to Alter Constraint
提问by user1777711
SQL How to Alter Constraint
SQL 如何改变约束
Below is 1 of my constraint
以下是我的约束之一
CONSTRAINT ACTIVEPROG_FKEY1 FOREIGN KEY(ActiveProgCode) REFERENCES PROGRAM(ActiveProgCode),
I want to add in
我想加入
ON DELETE CASCADE
to the constraint above.
到上面的约束。
How do i alter that existing constraint ACTIVEPROG_FKEY1 and add
我如何更改现有约束 ACTIVEPROG_FKEY1 并添加
ON DELETE CASCADE
to constraint ACTIVEPROG_FKEY1
约束 ACTIVEPROG_FKEY1
Consider ACTIVEPROG_FKEY1 is at Table ACTIVEPROG
考虑 ACTIVEPROG_FKEY1 在表 ACTIVEPROG
回答by user1819920
You can not alter constraints ever but you can drop them and then recreate.
您永远无法更改约束，但您可以删除它们然后重新创建。
Have look on this
看看这个
ALTER TABLE your_table DROP CONSTRAINT ACTIVEPROG_FKEY1;
and then recreate it with ON DELETE CASCADElike this
然后ON DELETE CASCADE像这样重新创建它
ALTER TABLE your_table
add CONSTRAINT ACTIVEPROG_FKEY1 FOREIGN KEY(ActiveProgCode) REFERENCES PROGRAM(ActiveProgCode)
ON DELETE CASCADE;
hope this help
希望这有帮助
回答by andy
No. We cannot alter the constraint, only thing we can do is drop and recreate it
不。我们不能改变约束，我们唯一能做的就是删除并重新创建它
ALTER TABLE [TABLENAME] DROP CONSTRAINT [CONSTRAINTNAME]
Foreign Key Constraint
外键约束
Alter Table Table1 Add Constraint [CONSTRAINTNAME] Foreign Key (Column) References Table2 (Column) On Update Cascade On Delete Cascade
Primary Key constraint
主键约束
Alter Table Table add constraint [Primary Key] Primary key(Column1,Column2,.....)
