Oracle-L: RE: WHERE 1 = 1 (any info on this)

From: April Wells <AWells_at_csedge.com>
Date: Tue, 21 Oct 2003 05:59:32 -0800
Message-ID: <F001.005D3DD1.20031021055932@fatcity.com>

BUT... a lot of the SQL still has rule hints in it for Apps... even though it is touted to be using the CBO extensively...

April Wells
Oracle DBA/Oracle Apps DBA
Corporate Systems
Amarillo Texas
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Few people really enjoy the simple pleasure of flying a kite Adam Wells age 11

-----Original Message-----
Sent: Tuesday, October 21, 2003 8:30 AM
To: Multiple recipients of list ORACLE-L

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)" <mike.hately_at_nedl.co.uk> 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. > > > > > > > >

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> > -- > Please see the official ORACLE-L FAQ: > http://www.orafaq.net > -- > Author: Hately, Mike (LogicaCMG) > INET: mike.hately_at_nedl.co.uk > > Fat City Network Services -- 858-538-5051 > http://www.fatcity.com > San Diego, California -- Mailing list and web > hosting services >
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Author: April Wells
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Received on Tue Oct 21 2003 - 08:59:32 CDT