Re: [HACKERS] More on GROUP BY

Tom Lane wrote:

> All true, but so what?  It wastes a few bytes of memory during
> planning, I suppose...

    Not  only  memory,  rewriting takes time too. If the GROUP BY
    clause has view columns, the rewriter has to change  all  the
    expressions  twice,  one time in the targetlist, another time
    in the group clause. Wasted efford if they  should  still  be
    equal after rewriting.

> I think it's true that using a TLE for each grouplist item is a waste of
> space, and that representing the grouplist as simply a list of expr's
> would be good enough.  But pulling out the TLE decoration seems like
> it's not an appropriate use of time at this stage of the release cycle.
> I'd say hold off till after 6.5, then fold it in with the parsetree
> redesign that you keep muttering we need (I agree!).

    I'm  sure  since  I  began to look at it that it's not such a
    good idea to make those changes at this stage.  But  in  fact
    some  of  them have to be done to make GROUP BY in views more
    robust.

>
> BTW, you keep using the term "RTE" which I'm not familiar with ---
> I assume it's just referring to the parse tree nodes?

    RTE == RangeTableEntry. The relations where the data  in  the
    querytree is coming from. The varno in Var nodes is the index
    into that table so the varno plus the varattno  identify  one
    relations attribute.


Jan

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