Date: Fri, 8 Jul 2005 10:32:15 -0600
From: Michael Fuhr <mike@fuhr.org>
To: Ying Lu <ying_lu@cs.concordia.ca>
Cc: pgsql-sql@postgresql.org
Subject: Re: Index creation question for expression (col1 || '-' || col2)
Message-ID: <20050708163215.GA81846@winnie.fuhr.org>
References: <42CEA509.3090507@cs.concordia.ca>
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In-Reply-To: <42CEA509.3090507@cs.concordia.ca>

On Fri, Jul 08, 2005 at 12:08:41PM -0400, Ying Lu wrote:
> 
> CREATE INDEX idx_t1 ON test (col1 || '-' || col2);
> 
> May I know is it possible and how I may create index for the expression 
> such as "col1 || '-' || col2" for a table please?

See "Indexes on Expressions" in the documentation:

http://www.postgresql.org/docs/8.0/static/indexes-expressional.html

"The syntax of the CREATE INDEX command normally requires writing
parentheses around index expressions, as shown in the second
example...."

That second example is exactly what you're trying to do:

CREATE INDEX people_names ON people ((first_name || ' ' || last_name));

-- 
Michael Fuhr
http://www.fuhr.org/~mfuhr/