From: | Greg Stark <gsstark(at)mit(dot)edu> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Functional dependencies and GROUP BY |
Date: | 2010-06-08 12:40:51 |
Message-ID: | AANLkTikc5yLDLHHiNJx3iYEuSswRUH_9tBSyl-hfEq0U@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Jun 8, 2010 at 4:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> I have developed a patch that partially implements the "functional
>> dependency" feature that allows some columns to be omitted from the
>> GROUP BY clause if it can be shown that the columns are functionally
>> dependent on the columns in the group by clause and therefore guaranteed
>> to be unique per group.
>
> The main objection to this is the same one I've had all along: it makes
> the syntactic validity of a query dependent on what indexes exist for
> the table. At minimum, that means that enforcing the check at parse
> time is the Wrong Thing.
It also needs to ensure that the plan is invalidated if the constraint
is dropped, which I assume amounts to the same thing.
--
greg
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