Horton

Re: wCTE behaviour

Dimitri Fontaine <dimitri@2ndquadrant.fr>

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From: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dimitri Fontaine <dimitri@2ndQuadrant.fr>, Yeb Havinga <yebhavinga@gmail.com>, Marko Tiikkaja <marko.tiikkaja@cs.helsinki.fi>, David Fetter <david@fetter.org>, pgsql-hackers@postgresql.org
Date: 2010-11-12T21:29:11Z
Lists: pgsql-hackers 
Tom Lane <tgl@sss.pgh.pa.us> writes:
> I can see that there's a fair argument for that position in cases like
> the above, but the trouble is that there are also cases where it's very
> hard for the user to predict how many rows will be read.  As examples,
> mergejoins may stop short of reading all of one input depending on what
> the last key value is from the other, and semijoins or antijoins will
> stop whenenever they hit a match in the inner input.

Oh. Indeed, I now understand what you mean by surprises. I keep
forgetting that DML and JOINs can live together…

Regards,
-- 
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support