Question

I have two SQL tables on SQL Server 2008 :

GameData 

GameID PK 
GameReleaseDate
GameTitle 
GameCoverClobID FK


GameClob

GameCoverClobID PK
Filename

So over time the covers are updated and whatnot, and as a result, I have several items in GameClob that have no matching ID in GameData are now effectively redundant data. I’d like to be able to delete these items, however I was wondering is there a SQL query that I can run, that will just show me the rows in GameClob that have no GameCoverClobID in the GameData table.

I hope I have explained this correctly, any questions, please ask.

Appreciate it!

Answer 1

Using the WHERE NOT EXISTS clause should be faster than LEFT JOIN and NOT IN because it shortcuts when the first record is found.

SELECT * 
FROM GameClob gc
WHERE NOT EXISTS (SELECT * 
                    FROM GameData gd 
                   WHERE gc.GameCoverClobID = gd.GameCoverClobID )

To prevent this problem in the future it is best to create a foreign key between the 2 tables

ALTER TABLE GameClob 
ADD CONSTRAINT fkGameClobGameData 
FOREIGN KEY (GameCoverClobID) 
REFERENCES GameData(GameCoverClobID)