>-----Original Message----- >From: Sándor Halász [mailto:h...@tbbs.net] >Sent: Monday, March 14, 2011 8:52 PM >To: Johan De Meersman >Cc: mysql@lists.mysql.com >Subject: Re: "IF" > >>>>> 2011/03/14 16:08 +0100, Johan De Meersman >>>> >I'm afraid I'm not authoritative on this, but it seems to me that it would be >very very bad if the third, unused expression were to be evaluated - not only >from a performance point of view, but who is to say that that expression is >not >a user-defined function that modifies the database ? ><<<<<<<< >Yes, but Access s "IIF", of the same use, evaluates all three, and the >documentation explicitly says so. MySQL s, that I have seen, says neither. >Assuming the worst is safer, and then one uses CASE ..., but if not, .... > > [JS] Also some optimizers (and I don't know if MySQL is that clever) will figure out which term is the cheapest to evaluate, and will change the order of evaluation.
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 >-- >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
