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Asked: 2026-06-08T11:53:50+00:00

I have one table called users with a PRIMARY key on users.zbid . However,

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I have one table called users with a PRIMARY key on users.zbid. However, all SELECT queries run on it include the WHERE clause cid='$cid' AND zbid='$zbid'. Should I add an index for cid or a multi-column index for cid,zbid ? I know the WHERE clause on cid seems redundant as zbid is PRIMARY, but it’s mainly there as a precautionary step, each cid designates a different forum, and in case something went wrong I don’t want every forum to be effected.

Secondly, I have another table called notifications. The only query that is run on this table uses the where clause cid='$cid' AND zbid='$zbid', should I add them both as individual indexes or just one? Why?

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1 Answer

  1. Editorial Team
    1. If you have primary key on users.zdib, there is no need for composite index (mysql will use the existing index on zdib)
    2. If cid is used in a similar way as in your first table, no need to have composite index, it should be enough just an index on zdib. Otherwise, make it on 2 columns.
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