From: Julian Scarfe <julian@avbrief.com>
To: pgsql-sql@postgresql.org
Subject: Negative lookbehind assertions in regexs
Date: Mon, 29 Aug 2005 14:11:37 +0100
Message-ID: <008901c5ac9b$31bb8b50$0600a8c0@Wilbur> (raw)
References: <001a01c5ac84$496fc750$1102a8c0@dream>
I'd like a regex that matches 'CD' but not 'ABCD' in any part of the regex.
In Perl I'd use a negative lookbehind assertion (?<!AB)CD to do the job:
$ cat lb.pl
print "CD: ", 'CD' =~ /(?<!AB)CD/, "\n";
print "XYCD: ", 'XYCD' =~ /(?<!AB)CD/, "\n";
print "ABCD: ", 'ABCD' =~ /(?<!AB)CD/, "\n";
$ perl lb.pl
CD: 1
XYCD: 1
ABCD:
But Postgresql (7.4) doesn't seem to like that:
# select 'ABCD' ~ '(?<!AB)CD';
ERROR: invalid regular expression: quantifier operand invalid
Is there a workaround that allows me to do this as a single regex?
I know I could and together a ~ and !~ like this
# select ('CD' ~ 'CD') and ('CD' !~ 'ABCD');
?column?
----------
t
(1 row)
# select ('ABCD' ~ 'CD') and ('ABCD' !~ 'ABCD');
?column?
----------
f
(1 row)
but changing the SQL would break the existing paradigm.
TIA
Julian
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-sql@postgresql.org
Cc: julian@avbrief.com
Subject: Re: Negative lookbehind assertions in regexs
In-Reply-To: <008901c5ac9b$31bb8b50$0600a8c0@Wilbur>
* 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