| From: | Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>, Yeb Havinga <yebhavinga(at)gmail(dot)com>, Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, David Fetter <david(at)fetter(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: wCTE behaviour |
| Date: | 2010-11-12 21:29:11 |
| Message-ID: | m28w0ytemw.fsf@2ndQuadrant.fr |
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| Lists: | pgsql-hackers |
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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