From: Tom Lane <tgl@sss.pgh.pa.us>
To: Theo Galanakis <Theo.Galanakis@lonelyplanet.com.au>
Cc: Pgsql-Sql@Postgresql. Org <pgsql-sql@postgresql.org>
Subject: Re: Regex
Date: Tue, 05 Oct 2004 23:36:29 -0400
Message-ID: <20759.1097033789@sss.pgh.pa.us> (raw)
In-Reply-To: <82E30406384FFB44AFD1012BAB230B5505F40D26@shiva.au.lpint.net>
References: <82E30406384FFB44AFD1012BAB230B5505F40D26@shiva.au.lpint.net>
Theo Galanakis <Theo.Galanakis@lonelyplanet.com.au> writes:
> Basically the regex should return TABLEA, TABLEB from:
> Select *
> from TABLEA
> Inner jon TABLEB on tableb.columna = tablea.columna
You realize of course that this problem is mathematically impossible?
Regexes are less powerful than context-free grammars, and so it is a
certainty that there exist legal SQL statements that will fool any regex
that you invent for this purpose.
If you know that the SQL statements are coming from a query generator
that produces only a certain style of SQL code, then you might be able
to come up with a solution that works reliably for the output of that
query generator. But I wonder if you wouldn't be better off bypassing
the parse-and-deparse hacking and tapping directly into the query
generator.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, Theo.Galanakis@lonelyplanet.com.au
Subject: Re: Regex
In-Reply-To: <20759.1097033789@sss.pgh.pa.us>
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