From: Tom Lane <tgl@sss.pgh.pa.us>
To: Torsten Grust <torsten.grust@gmail.com>
cc: pgsql-sql <pgsql-sql@lists.postgresql.org>,
        Gary Stainburn <gary.stainburn@ringways.co.uk>
Subject: Re: select into composite type / return
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>
Comments: In-reply-to Torsten Grust <torsten.grust@gmail.com>
	message dated "Thu, 18 Mar 2021 12:10:06 +0100"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <3718234.1616077713.1@sss.pgh.pa.us>
Date: Thu, 18 Mar 2021 10:28:33 -0400
Message-ID: <3718235.1616077713@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/3718235.1616077713%40sss.pgh.pa.us>
Precedence: bulk

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