From: Tom Lane <tgl@sss.pgh.pa.us>
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: harry@harryclarke.me.uk, PostgreSQL Documentation <pgsql-docs@lists.postgresql.org>
Subject: Re: text and varchar are not equivalent
Date: Fri, 09 Feb 2024 12:51:51 -0500
Message-ID: <1694198.1707501111@sss.pgh.pa.us> (raw)
In-Reply-To: <CAKFQuwbUeWu8fp5J1FW2vBn8-5RGnVS+Jtdri38HJbYT+VLPmA@mail.gmail.com>
References: <170747750218.3279716.17734031485916520031@wrigleys.postgresql.org>
<CAKFQuwbUeWu8fp5J1FW2vBn8-5RGnVS+Jtdri38HJbYT+VLPmA@mail.gmail.com>
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Fri, Feb 9, 2024, 10:12 PG Doc comments form <noreply@postgresql.org>
> wrote:
>> The documentation implies that the data types text and varchar are
>> equivalent, but this is not the case with this test in Postgresql version
>> 16.
> Fair point. But I'd rather further emphasize that char should just be
> avoided so this and other unexpected outcomes simply do not manifest in a
> real database scenario. Rather than try and document how odd it's behavior
> is when dealing with intra-textual type conversions.
Yeah, this is less about varchar acting oddly and more about char
acting oddly. The short answer though is that text is a preferred
type, varchar is not, and that makes a difference when resolving
whether to apply text's or char's equality operator. You can
detect how it's being handled with EXPLAIN:
regression=# explain verbose SELECT vc = ch AS vc_ch FROM test;
QUERY PLAN
---------------------------------------------------------------
Seq Scan on pg_temp.test (cost=0.00..17.88 rows=630 width=1)
Output: ((vc)::bpchar = ch)
(2 rows)
regression=# explain verbose SELECT txt = ch AS txt_ch FROM test;
QUERY PLAN
---------------------------------------------------------------
Seq Scan on pg_temp.test (cost=0.00..19.45 rows=630 width=1)
Output: (txt = (ch)::text)
(2 rows)
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-docs@postgresql.org
Cc: tgl@sss.pgh.pa.us, david.g.johnston@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: text and varchar are not equivalent
In-Reply-To: <1694198.1707501111@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox