On Saturday 01 March 2003 01:26, Henning Schulzrinne wrote:
> Both email columns have the same format (varchar) and are indexed
> individually:
>
> describe SELECT person FROM person WHERE email1='foo' OR email2='foo';
> +--------+------+---------------+------+---------+------+-------+----------
>---+
>
> | table | type | possible_keys | key | key_len | ref | rows | Extra
>
> +--------+------+---------------+------+---------+------+-------+----------
>---+
>
> | person | ALL | email1,email2 | NULL | NULL | NULL | 57051 | Using
>
> where |
> +--------+------+---------------+------+---------+------+-------+----------
>---+
[skip]
> I'm curious why this is. (In general, I have been surprised by how often
> indices are not used even if they exist.)
it's know behaviour and described in the manual:
http://www.mysql.com/doc/en/MySQL_indexes.html
http://www.mysql.com/doc/en/Searching_on_two_keys.html
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