检查同一表中对唯一列的约束引用

Question

I have a table:

ID     Name       ParentID
==     ====       ========
1       A          Null
2       B           1
3       C           2

so A is parent of B, and B is parent of C.

I need to create a constraint for column(ParentID) which does not accept a number is not exist in column (ID). How I would do that?

Answer 1

You need to add Foreign Key.

ALTER TABLE table1 
  ADD CONSTRAINT fk_parent_id 
  FOREIGN KEY (parent_id) REFERENCES table1(id);

Answer 2

You can also create a foreign key using SSMS design as shown below. Expand table and right click on Keys - New Foreign key

Now click on the browse button of relationship and specify the colum nane of primary and foreign key table as shown below.

This is one of the way and you might select the preferred way either using query or design for creating the foreign key relationships between tables in Sql Server.