Re: substring synopsis section, third argument is optional doc didn't show that

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: jian he <jian(dot)universality(at)gmail(dot)com>
Cc: pgsql-docs(at)lists(dot)postgresql(dot)org
Subject: Re: substring synopsis section, third argument is optional doc didn't show that
Date: 2025-01-21 16:53:24
Message-ID: 3354664.1737478404@sss.pgh.pa.us
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-docs

jian he <jian(dot)universality(at)gmail(dot)com> writes:
> https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-SIMILARTO-REGEXP

> """
> or as a plain three-argument function:
> substring(string, pattern, escape-character)
> """

> but here "escape-character" is optional.

> substring(string, pattern [,escape-character])
> would be more accurate.

No, the text is correct as written. substring(text, text) is a
completely different function that implements POSIX regular
expressions, not SQL regular expressions. It's described in
the next section (9.7.3). For example,

regression=# select substring('foobar', 'o.b');
substring
-----------
oob
(1 row)

regression=# select substring('foobar', 'o.b', '');
substring
-----------

(1 row)

because '.' is a metacharacter in POSIX but not SQL regexps.

regards, tom lane

In response to

Responses

Browse pgsql-docs by date

  From Date Subject
Next Message Tom Lane 2025-01-21 17:26:03 Re: Request for Formal Syntax of WHERE Clause Conditions
Previous Message PG Doc comments form 2025-01-21 16:01:59 Request for Formal Syntax of WHERE Clause Conditions