It is absolutely not necessary to build any indexes which already have the same key fields in the the same order in another index. The optimizer looks and sees which index most closely matches the criteria laid out in the SQL statement and will use the one with the lowest cost.
Date: Thu, 10 Jul 2014 20:16:44 +0200
Subject: table indexes
I have a table with an index already on Columns 1, 2, 3 and 4.
Now I've been told we need another one on Columns 1, 2 and 3.
Is that necessary? I don't see why.
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