Re: Regex

Thanks Tom, 
        I attacked the issue another way which appears to work... 
        I used :
        explain select * from nodes left join node_names on node_names.node_id = nodes.node_id
        which returned :
        query 
          QUERY PLAN 
        1 Merge Right Join (cost=429.16..793.48 rows=4510 width=193) 
        2 Merge Cond: ("outer".node_id = "inner".node_id) 
        3 -> Index Scan using node_names_node_id_key on node_names (cost=0.00..278.58 rows=                     7253 width=110) 
        4 -> Sort (cost=429.16..438.89 rows=3894 width=83) 
        5 Sort Key: nodes.node_id 
        6 -> Seq Scan on nodes (cost=0.00..196.94 rows=3894 width=83) 
        
        and then programatically searched for lines that begin with :
        Seq Scan on #table_name#
        Index Scan using #indexname# on #table_name#
        obtaining the #table_name#
        Being : nodes, node_names
Theo
-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us] 
Sent: Wednesday, 6 October 2004 1:36 PM
To: Theo Galanakis
Cc: Pgsql-Sql@Postgresql. Org
Subject: Re: [SQL] Regex 
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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