Feedback-ID: david@calascibe
Reply-To: <David@Calascibetta.com>
From: "David M. Calascibetta" <david@calascibetta.com>
To: <pgsql-bugs@lists.postgresql.org>
References: <17258-a7c164c5fb955221@postgresql.org>
 <19D58355-E7C3-47D7-9C87-51EC751AE2BB@enterprisedb.com> 
In-Reply-To: 
Subject: FW: BUG #17258: Unexpected results in CHAR(1) data type
Date: Fri, 29 Oct 2021 14:32:48 -0500
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-----Original Message-----
From: David M. Calascibetta <david@calascibetta.com>=20
Sent: Friday, October 29, 2021 2:04 PM
To: 'Mark Dilger' <mark.dilger@enterprisedb.com>
Subject: RE: BUG #17258: Unexpected results in CHAR(1) data type

Ok, but my example was just a simplified version of what is going on.
The actual problem stems from a CHAR(1) column data type that is =
behaving the same way.
I was just trying to create a super-simple example of the problem.
It still seems to me that a CHAR(1) should never be zero length, =
regardless of how it's implemented.


-----Original Message-----
From: Mark Dilger <mark.dilger@enterprisedb.com>=20
Sent: Friday, October 29, 2021 1:58 PM
To: david@calascibetta.com; PostgreSQL mailing lists =
<pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17258: Unexpected results in CHAR(1) data type


> On Oct 29, 2021, at 11:14 AM, PG Bug reporting form =
<noreply@postgresql.org> wrote:
>=20
> select length(substr('   '::varchar,1,1)), ascii(substr(' =20
> '::varchar,1,1));
> produces=3D=3D> 1    32   (as expected)
>=20
> select length(substr('   '::char,1,1)), ascii(substr('   =
'::char,1,1));
> produces=3D=3D> 0     0     (not as expected)

There are four substr() functions defined in the standard distribution.  =
They are:

  substr(text, int4, int4)
  substr(text, int4)
  substr(bytea, int4, int4)
  substr(bytea, int4)

There is none defined directly for char(n).  Since "text" is the =
preferred type (not "bytea"), I expect a cast of your ' '::char to text =
before entry to the function.  So the question is why casting ' '::char =
to text is different than ' '::text.  The answer is that cast is =
implemented using rtrim1, which trims trailing space.

=E2=80=94
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL =
Company