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Martijn van Oosterhout wrote:
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> On Mon, Sep 04, 2006 at 05:15:57PM +0100, Mark Cave-Ayland wrote:
> > 3) Add planner support so that WITH clauses are mapped to a new type of
> > node that utilises two tuplestores - an output tuplestore and a working
> > tuplestore. The output tuple store will in effect be the contents of the
> > table expression while the working tuplestore holds the results of the
> > last iteration if recursive. Also implement some kind of WithState node
> > which keeps track of the recursion state.
>
> That's basically what I came up with. Basically you have a sort of loop
> in the execution plan where tuples that come out are copied into a
> tuplestore and run through a particular part of the executor again. The
> top-down approach of the executor makes it a bit trickier...
>
> > Having spent some more time today looking at 1) and also at the SQL 2003
> > spec, it would seem that other databases offer the WITH clause within
> > subqueries and also as part of a view. I'd be interested to hear
> > feedback from other developers as to whether it would be possible to
> > achieve this level of support within PostgreSQL.
>
> Absolutly possible. The question is how much work :)
>
> Incidently, if you find a way to support common subplans (where a part
> of the executor is shared between two executions) that might provide a
> way to solve some of the trickier multiple evaluation problems with
> rules. Again, it would just be a tuplestore the stored the results for
> multiple executions.
>
> Have a nice day,
> --
> Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
> > From each according to his ability. To each according to his ability to litigate.
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-- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB
http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
