From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Geoff Winkless <pgsqladmin(at)geoff(dot)dj> |
Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Postgres General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: COALESCE requires NULL from scalar subquery has a type |
Date: | 2016-02-09 14:53:02 |
Message-ID: | 5636.1455029582@sss.pgh.pa.us |
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Lists: | pgsql-general |
Geoff Winkless <pgsqladmin(at)geoff(dot)dj> writes:
> I'm not asking that it coerce an actual value with a genuinely unknown
> type to a text value: I'm simply suggesting that it's unnecessary for
> COALESCE to coerce an unknown-typed NULL into anything (even if you
> ignore that NULL is, as far as I know, equivalent, no matter what its
> type), because as far as COALESCE is concerned the NULL can be
> instantly ignored.
Leaving aside the question of whether that is actually feasible or
a good idea: how would that improve your original complaint?
SELECT COALESCE((SELECT 'Yes' FROM gwtest WHERE id=4), 'No') AS valid;
There's no null visible anywhere in that. I suppose that if there's
no row with id=4, there would be a null at runtime, but that's not
going to make any difference for parse-time determination of what
type the COALESCE() will return.
regards, tom lane
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