On Thu, 2009-02-05 at 08:48 +1100, Chris wrote: > Ashley Sheridan wrote: > > On Thu, 2009-02-05 at 08:38 +1100, Chris wrote: > >> Jônatas Zechim wrote: > >>> For example i’ve this query: > >>> > >>> > >>> > >>> SELECT admin_nome FROM ctalk_admin WHERE admin_lastping <= '1233762658' > >>> AND > >>> admin_lastping >= '1233762608' AND admin_id='1' > >>> > >>> > >>> > >>> I ran explain, the result for extra is ‘Impossible WHERE noticed after > >>> reading const table...’ > >> Well this one is impossible. > >> > >> Find records with ping before '1233762658' AND > >> find records with ping after '1233762608' > >> > >> The before time is before the after time. > >> > >> -- > >> Postgresql & php tutorials > >> http://www.designmagick.com/ > >> > >> > > Erm, I don't think so, notice that 5 as the second to last digit. He > > wants to find a ping before the larger number and after the smaller > > number, which is perfectly valid in the normal rules of the universe I > > know ;) > > *bangs head on desk* > Going to be a long day... > > Either way, mysql knew this query couldn't return any results for some > reason (hence "impossible where noticed"), so using this as an example > when trying to optimize will fail. > > -- > Postgresql & php tutorials > http://www.designmagick.com/ > > MySQL may have noticed it was impossible with the current data he had using the index on that field, but in the future it may become valid, so I wouldn't necessary eliminate it if it's deemed crucial. A query that returns no results is equally as useful as one that returns many.
Ash www.ashleysheridan.co.uk -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
