Oracle-L: RE: type of join in sql

From: Grabowy, Chris <cgrabowy_at_fcg.com>
Date: Fri, 26 Jul 2002 06:38:17 -0800
Message-ID: <F001.004A34DF.20020726063817@fatcity.com>

bp,

Checkout a white paper entitled: A Look Under The Hood of CBO: The 10053 Event. You can find this whitepaper on the hotsos.com website. Your probably going to be looking at the General Plans section of the trace.

Goodluck.

Chris

"BigP" <big_planet_2000_at_hotmail.com>
Sent by: root_at_fatcity.com
07/23/2002 06:58 PM
Please respond to ORACLE-L

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
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        Subject:        type of join in sql

can some body shed some light on how does the optimizer decides to choose the kind of join i.e. nested loop, sort merge or hash join . In one of queries if i tweak the join condition it changes the type of join and start using index , otherwise it doesn't . I thought it depends on statistics .. if optimize finds that are more qualifying records in inner table then it will prefer to go for sort merge and will do full scan of inner table , but if it thinks there are less records in inner table it will user nested loop . am I correct ?

TIA ,
bp

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Author: Grabowy, Chris
INET: cgrabowy_at_fcg.com

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