From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
cc: t.dnil@yahoo.com, pgsql-docs@lists.postgresql.org
Subject: Re: COALESCE doccumentation
In-reply-to: <20190429231305.ra5z5bapif353vdx@momjian.us>
References: <155639681797.1368.1856073093791885251@wrigleys.postgresql.org>
 <20190429231305.ra5z5bapif353vdx@momjian.us>
Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
	message dated "Mon, 29 Apr 2019 19:13:05 -0400"
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Date: Mon, 29 Apr 2019 21:33:46 -0400
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Bruce Momjian <bruce@momjian.us> writes:
> On Sat, Apr 27, 2019 at 08:26:57PM +0000, PG Doc comments form wrote:
>> Try, for example. 
>> 
>> SELECT COALESCE(NULL, '12', 3, 1, 1); -- OK!
>> SELECT COALESCE(NULL, '12.2', 3.2, '1', 1.1); -- OK!
>> SELECT COALESCE(NULL, '1d2', 3, 1, 1); -- error
>> SELECT COALESCE(NULL, '12', 3, '1d', 1); -- cast error

> What is wrong about the existing description?  That it doesn't mention
> mixing data types?

The place where that behavior is described is

https://www.postgresql.org/docs/current/typeconv-union-case.html

It doesn't mention COALESCE explicitly, though ... and I imagine
digging in the code for coerce_to_common_type callers might find
some other cases that aren't listed there.

			regards, tom lane