That did the trick. Thank you for the quick detailed answer. It runs in about a minute now.
Jeff Barrett "Stephan Szabo" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > On Fri, 21 Sep 2001, Jeff Barrett wrote: > > > I have a select statement that returns a set of 74,000+ results back in > > under a minute as follows: > > > > select s.sessid, s.membid, s.datetime > > from sessions2 s, (select min(datetime) as datetime, membid > > from sessions2 > > where membid is not null > > group by membid) as minsess > > where s.membid = minsess.membid > > and s.datetime = minsess.datetime; > > > > The final cost from explain for the above select is 22199.15 ... 24318.40 > > with rows = 5 and width = 28. > > > > Then I issue an update as follows (to update those 74,000+ rows): > > update sessions2 set sinceinception = 0 > > from sessions2 s, (select min(datetime) as datetime, membid from sessions2 > > group by membid) as mindate > > where s.membid = mindate.membid > > and s.datetime = mindate.datetime; > > > > The final cost from explain for the above update is 31112.11...98869.91 with > > rows = 2013209 and width=87. > > > > This update statement has been left running over night and does not > > complete. The ram usage on the machine is at about 3/4 capacity (800mb) > > during this time and CPU usage is near 100%. The machine has the -F option > > set and memory segments of 200mb and is running 7.1.2. > > > > What could be causing this update statement to not complete? > > Why are the costs so different since it seems to me that besides the cost of > > the update they are the same query? > > I thought that the updated table is always in your from list (implicitly), > so you'd want: > update sessions2 set sinceinception = 0 > from (select min(datetime) as datetime, membid from sessions2 group by > membid) as mindate > where sessions2.membid=mindate.membid and > sessions2.datetime=mindate.datetime; > > I think your query would be joining the s/mindate results against > sessions2. > > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to [EMAIL PROTECTED] so that your > message can get through to the mailing list cleanly ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
