OK, here's the interesting thing. At 8.1.6.3 with optimizer_mode=rule the statement I'm looking at returns very different explain plans depending on whether the "1=1" clause is included. It's a complicated join and the explain plans are over 300 lines so it's not easy to see what's happening. I'll try with a simpler join. And yes, I know the RBO is ancient technology these days. =)
Cheers, Mike -----Original Message----- Sent: 21 October 2003 12:05 To: Multiple recipients of list ORACLE-L I'm pretty sure the optimizer can pick up 1=1 anyway and ignore it as an always-true condition - so you get no benefit. The most common cause I've seen for 1=1 is so when developers are building dynamic where-clause, they don't need to worry about adding 'where' versus 'and' to the sql string being constructed. hth connor --- "Hately, Mike (LogicaCMG)" <[EMAIL PROTECTED]> wrote: > Morning folks, > > the developers here are looking at a view with a > where clause which > specifies : > > WHERE 1=1 AND > ............... AND > ............... etc. > > I'd seen this used before as a way of tweaking the > RBO into certain > behaviours but it was years ago and my recollection > is very hazy. > The only explanation I've found so far is : > > "the 1=1 is in there to avoid doing repetitive index > scans for single > rowids, when the app "knows" the result set is going > to be manipulated > rowid's for a large subset of the table. I would > guess your DUAL/CBO example > had some similar effect." > > Is anyone familiar enough with this tweak to explain > it ? > > Cheers, > Mike > > PS Maybe it'll head off some replies if I make it > clear that this view > hasn't been generated by code so the "1=1" isn't an > accidental artifact It > was custom written and is definitely supposed to > have exactly this > structure. > > > > > > > > **************************************************************************** **************** > E mail Disclaimer > > You agree that you have read and understood this > disclaimer and you agree to be bound by its terms. > > The information contained in this e-mail and any > files transmitted with it (if any) are confidential > and intended for the addressee only. 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