* Eldon Ziegler > > mysql is slow when finding the last value before a period of time (I'm > plotting the temperature values during a period of time and want the last > value before the period begins). > > The query is: > select DateTime, Target, Value from log > where DateTime < "2001-12-21 00:00:00" > and Source = "StatIO#1" > and Target = "SN1" > and (Attribute = NULL or Attribute = "" or Attribute = "T") > order by DateTime desc limit 1; > > The table has two indexes, > 1. DateTime only > 2. dtSrcTarAttr on log (DateTime, Source, Target, Attribute) > > "Explain" shows the query using the DateTime index instead of the > dtSrcTarAttr that contains all items in the WHERE clause. > > How can I speed up this query?
Change (DateTime, Source, Target, Attribute) to (Source, Target, DateTime, Attribute) -- Roger --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
