>> SELECT COUNT(*) AS num FROM alerts WHERE stamp > DATE_SUB(NOW(),
>> interval 300 second) AND devid=244;
>> With this query, MySQL will run DATE_SUB() once, and then use the
>> index on stamp (which I assume you have) to narrow down the result set.
[JS] I don't understand how an index on a timestamp would help. Theoretically,
each record could have a unique value for the timestamp; so the index would
have an entry for each record. Would MySQL really use that in preference to,
or in combination with, an index on devid?
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>That did it! Thank you.
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