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(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Wednesday, 6 October 2004 1:36 PM
To: Theo Galanakis
Cc: Pgsql-Sql(at)Postgresql(dot) Org
Subject: Re: [SQL] Regex

Theo Galanakis <Theo(dot)Galanakis(at)lonelyplanet(dot)com(dot)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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