On 1/14/11 3:52 AM, Bruce Ferrell wrote:
select count(*) as count
from alerts where (unix_timestamp(stamp)> (unix_timestamp(now()) -
'300' ) )
and devid = '244';
Bruce -
The problem is that the index is useless, because you're running a
function on the timestamp. What you want is this:
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.
Steve
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