MS SQL Server Interview Question:

What Happens If You Insert a Duplicate Key for the Primary Key Column in MS SQL Server?

Submitted by: Administrator

If your table has a primary key column, and you are trying to insert a new row with duplicate key value on the primary key column, you will get an error. The reason is simple - Primary key column does not allow duplicate values. The following tutorial exercise gives you a good example:

SELECT * FROM ggl_links
INSERT INTO ggl_links VALUES (101,
'www.globalguideline.com',
NULL,
0,
'2006-04-30')
GO
Msg 2627, Level 14, State 1, Line 1
Violation of PRIMARY KEY constraint
'PK__ggl_links__03317E3D'. Cannot insert duplicate
key in object 'dbo.ggl_links'.
The statement has been terminated.

You are getting this error, because value "101" has already been used by an existing row.
Submitted by: Administrator