I need to find out who has the same values across three columns for Users' who joined before a certain date.
SELECT * FROM tblUser u1 INNER JOIN tblUser u2 ON u2.UserTypeID=u1.UserTypeID AND u2.MasterClubID=u1.MasterClubID AND u2.SiteSkinID=u1.SiteSkinID WHERE u1.DateJoined<=01/01/2006
Is multiple column joins a legitimate way of grabbing data? Does it have any significant impact on performance?
Is multiple column joins a legitimate way of grabbing data?
Absolutely. If it's appropriate to fulfill your requirements it should narrow down the returned dataset.
quote:Originally posted by ElCapitan
Does it have any significant impact on performance?
The dreaded "It depends". Are your indexes appropriate for the join? Are they up-to-date i.e. little fragmentation, statistics updated recently? How much data is contained in the 2 tables? Check out the execution plan for more info as well.
Now, as far as your posted query returning the result set that you seem to want, I don't believe it will - but give it a go and see what you get. If it does not work as expected, post some sample data and what the expected results should be and we can help.
Thanks for your reply. If it is a legit way of grabbing data then I am happy to continue with designing the schema of the database knowing that it is ok (in this one circumstance) to get data this way. The query I showed was just a sample to demonstrate my intention. Thank you for confirming that type of query is ok even though in the example not quite realistic.
I shall post back to this thread if I have any other questions if you could subscribe to this topic. Thanks again for your time.
INNER JOIN on Multiple columns
Posted - 03/24/2009 : 09:40:53
