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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Torsten Grust <torsten.grust@gmail.com>
Cc: pgsql-sql <pgsql-sql@lists.postgresql.org>
Cc: Gary Stainburn <gary.stainburn@ringways.co.uk>
Subject: Re: select into composite type / return
Date: Thu, 18 Mar 2021 10:28:33 -0400
Message-ID: <3718235.1616077713@sss.pgh.pa.us> (raw)
In-Reply-To: <CAGqkgphmj3uHB3Jc5Eb=yA2cfffHFsACWR3Fbfr6jrkQepKJPA@mail.gmail.com>
References: <39dcfab9-4eb2-382b-9186-baf722ca56a0@ringways.co.uk>
	<3523853.1616002010@sss.pgh.pa.us>
	<9eb42b06-9cfa-1e4b-e42b-6f64e99675a5@ringways.co.uk>
	<7af5d693-a6a3-d3d4-050a-0898aad8bd77@ringways.co.uk>
	<CAGqkgphmj3uHB3Jc5Eb=yA2cfffHFsACWR3Fbfr6jrkQepKJPA@mail.gmail.com>

Torsten Grust <torsten.grust@gmail.com> writes:
> Hi Gary,
> a shot in the dark but maybe

> SELECT id, (do_breakdown(id)).*
> FROM   ...

> already does the job?

Beware --- what that actually does is expand into

SELECT id, (do_breakdown(id)).f1, (do_breakdown(id)).f2, ...

so that the function will be invoked N times if it produces N columns.

What you generally want to do is invoke the function as a lateral FROM
item:

SELECT id, f.* FROM table AS t, LATERAL do_breakdown(t.id) AS f;

			regards, tom lane

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