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From:Sasha Pachev Date:May 11 1999 4:23am
Subject:Re: Simple Indexing Question...
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Hank Eskin wrote:
> Easy question:
>   I have a datetime column in a table of 150,000 rows,
> and I want to query records for a certain day AND use
> the index on the column.. Anytime I do this:
> SELECT * FROM tables where TO_DAYS(NOW()) = TO_DAYS(entry_time) ;  <today's
> records>
> Or
> SELECT * FROM tables where TO_DAYS(entry_time) = 730249;
>      <records for some other day, using from_days() function)>
> The explain does not use the index on entry_time, and I don't want to add
> another column just for day number..
> Thanks in advance!

The problem is that MySQL cannot use the index on an expression in where
clause. Think of re-writing the where clause of your query in the form
of constant = entry_time.

Sasha Pachev
Simple Indexing Question...Hank Eskin11 May
  • Re: Simple Indexing Question...Sasha Pachev11 May