From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Dilger <mark.dilger@enterprisedb.com>
Cc: " <David@calascibetta.com>
Cc: " <David@Calascibetta.com>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17258: Unexpected results in CHAR(1) data type
Date: Fri, 29 Oct 2021 18:23:27 -0400
Message-ID: <758069.1635546207@sss.pgh.pa.us> (raw)
In-Reply-To: <F04C22E4-C392-446E-840E-264F77397945@enterprisedb.com>
References: <17258-a7c164c5fb955221@postgresql.org>
<19D58355-E7C3-47D7-9C87-51EC751AE2BB@enterprisedb.com>
<003701d7ccfb$c2a85bb0$47f91310$@calascibetta.com>
<0EE9669C-6E65-40E1-B492-F989F452DAC4@enterprisedb.com>
<005501d7cd0b$9ba5d5f0$d2f181d0$@calascibetta.com>
<F04C22E4-C392-446E-840E-264F77397945@enterprisedb.com>
Mark Dilger <mark.dilger@enterprisedb.com> writes:
> I haven't studied the behavior of char(n) on other RDBMS products. I'd be curious if the SQL spec says anything that we're violating in this regard.
It's not a great approximation to the spec. Postgres views trailing
spaces in a char(n) value as always being semantically insignificant,
where I think the spec treats them as insignificant only for purposes of
comparisons. Even more to the point, the spec considers that PAD SPACE
is an attribute of *collations* not data types. Back in the day we
didn't have collations, so the only way to even approximate that
behavior was to make it a data type property. Now that we do have
collations, it'd be conceivable to reimplement all this in something
closer to the way the spec describes it. But it'd be a lot of work,
and I'm not sure we'd accept such a patch even if somebody wrote it.
It'd almost inevitably break applications that are relying on the
existing behavior.
> I tend to think of char(n) as a misfeature and avoid using it.
Yeah, that. I haven't seen any reason to use char(n) rather than
varchar(n) since punched cards stopped being a thing. So it's hard
to summon the motivation to do a lot of work on that data type.
Perhaps somebody else will feel more motivated, but nobody's stepped
forward, and I wouldn't counsel holding your breath for it.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, mark.dilger@enterprisedb.com, David@calascibetta.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17258: Unexpected results in CHAR(1) data type
In-Reply-To: <758069.1635546207@sss.pgh.pa.us>
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