From: hsv
Date: October 16 2012 5:38pm
Subject: Re: mysql logs query with indexes used to the slow-log and not
  logging if there is index in reverse order
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>>>> 2012/10/16 12:57 -0400, Michael Dykman >>>>
your now() statement is getting executed for every row on the select.  try
ptting the phrase up front
as in:
set @ut= unix_timestamp(now())
and then use that in your statement.
<<<<<<<<
Quote:

Functions that return the current date or time each are evaluated only once per query at the start of query execution. This means that multiple references to a function such as <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functions.html#function_now>NOW() within a single query always produce the same result. (For our purposes, a single query also includes a call to a stored program (stored routine, trigger, or event) and all subprograms called by that program.) This principle also applies to <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functions.html#function_curdate>CURDATE(), <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functions.html#function_curtime>CURTIME(), <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functions.html#function_utc-date>UTC_DATE(), <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functions.html#function_utc-time>UTC_TIME(), <file:///C:/Program%20Files/MySQL/MySQL%20Server%205.5/HELP/functio
ns.html#function_utc-timestamp>UTC_TIMESTAMP(), and to any of their synonyms.