<snip> >> >> 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?
Regards, Jerry Schwartz Global Information Incorporated 195 Farmington Ave. Farmington, CT 06032 860.674.8796 / FAX: 860.674.8341 E-mail: je...@gii.co.jp Web site: www.the-infoshop.com >> Steve >> >That did it! Thank you. > >-- >MySQL General Mailing List >For list archives: http://lists.mysql.com/mysql >To unsubscribe: http://lists.mysql.com/mysql?unsub=je...@gii.co.jp -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
