Thanks for the question, Pierre.
Asked: May 07, 2006 - 4:56 pm UTC
Last updated: May 08, 2006 - 10:11 am UTC
Version: 9.2
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Hi Tom,
Suppose we have a slow SELECT query with several joined tables that don't have foreign keys constraints but they should have.
Now we create the missing foreign keys constraints: and that's the only change. Can these FK creation change something for the execution plan ? If yes, what ? Can the query run really faster ? Is it true in some cases or never true ?
Sorry for not having full example: this is something I've read in a forum and I would like to have your opinon about that.
Thanks !
and Tom said...
Well, if you also had materialized views - we would use the constraints to enable the use of query rewrite more frequently (so yes, in general, the more constraints the better - the optimizer uses this information).
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It could be true, yes. Depends on the physical structures you have in place and whether the newly added constraint allows us to use them more efficiently.