query,updates,iso. levels

Hi, Suppose I have large query which takes a long time to run since it reads a huge data set. If there is a second small,short query which begins after the first query began and if it updates a portion of the first queries data set, Will the first query use old un-updated values or updated values ? would the isolation levels matter in this case ? Thanks, Sathish Sent via Deja.com http://www.deja.com/

Well actually , I am looking to simulate the way oracle returns data and the equivalent of Oracle's 'SET TRANSACTION READ ONLY', where the data returned by a query is what existed when the query began,even if there were updates to its data set while the query was executing. In Informix if I were to set Query 1 (the big select query) at an Isolation of 'Repeatable Read', then the second query will not be able to update (if both queries are looking at the same data), or the second query would have updated rows before the first gets to that part of the data.So,..., how would I retrieve data as it existed when the query began and still allow other subsequent queries do updates against the same table. Thanks, Sathish S >From: "Parker, Jack" <JParker@Engage.com> >To: sathish_sadagopan@my-deja.com >Subject: RE: query,updates,iso. levels >Date: Thu, 1 Feb 2001 12:35:58 -0500 > >It depends. If you are using an isolation level which insists that it >be >able to return the same values from the table (Repeatable Read), then >each >row you read will be locked (unless you have a table or page lock level >set) >and your second query will not be allowed to change the data. >Otherwise, >the data will be read as it stands. If a row was read before the >second >query updated it, then you would get the old value, if after the >update, >then you would get the new value. > >cheers >j. In article <95br6b$k1f$1@nnrp1.deja.com>, sathish_sadagopan@my-deja.com wrote: > Hi, > Suppose I have large query which takes a long time to run since it > reads a huge data set. > If there is a second small,short query which begins after the first > query began and if it updates a portion of the first queries data set, > > Will the first query use old un-updated values or updated values ? > would the isolation levels matter in this case ? > Thanks, > Sathish > > Sent via Deja.com > http://www.deja.com/ > Sent via Deja.com http://www.deja.com/