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We are having a debate in our company. I use left outer joins quit frequently. I was told by another programmer that there is too much over head and I should not use them. Example, Lets say I have two tables, they would rather me hit the database twice get the information I need from each table store it in memory and join the data on the java side, instead of just doing a left outer join. I think this is absurd and would be bad for performance. Am I wrong
We used to do joins in the application rather than in the database sometimes back in the 80s. But really, by 1988 or so the database optimizer was usually good enough with DB2 that wasn’t necessary any more.
I can’t think of any ordinary scenarios that warrant application-joins. Abnormal situations like when you’ve got an over-loaded database server, fat network pipe, a ton of capacity on the app server, and a bunch of new queries – might warrant it for some of the queries. Maybe.
But in general joins, including left/right/full outer joins are your friend. They allow you to have smaller tables, get better use out of both storage and memory, etc. But you do want up to date statistics, to have a passing familiarity with the kinds of access paths a database uses and get in the habit of doing explains.