Date: Thu, 29 Aug 2013 06:43:57 -0700 (PDT)
From: David Johnston <polobo@yahoo.com>
To: pgsql-sql@postgresql.org
Message-ID: <1377783837680-5768926.post@n5.nabble.com>
In-Reply-To: <1377781964520-5768923.post@n5.nabble.com>
References: <k8vmbm$1fg$1@ger.gmane.org>
 <E72D307E-D276-4FF6-8E05-8434C6370AB8@yahoo.com>
 <1377781964520-5768923.post@n5.nabble.com>
Subject: Re: Using regexp_matches in the WHERE clause
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spulatkan wrote
> so following is enough to get the rows that matches regular expression

> 

This is bad form even if it works.  If the only point of the expression is
to filter rows it should appear in the WHERE clause.  The fact that
regexp_matches(...) behaves in this way at all is, IMO, a flaw of the
implementation.


> on pgadmin the column type is shown as text[] thus I also do not
> understand why array_length on where condition does not work for this.

> 

This works because the array_length formula is applied once to each "row" of
the returned set.  

As mentioned before it makes absolutely no sense to evaluate a set-returning
function within the WHERE clause and so attempting to do so causes a fatal
exception.  For my usage I've simply written a wrapper function that
implements the same basic API as regexp_matches but that returns a scalar
"text[]" instead of a "setof text[]".  It makes coding these kinds of
queries easier if you know/understand the fact that your matching will never
cause more than 1 row to be returned.  If zero rows are returned I return an
empty array and the normal 1-row case returns the matching array.

David J.


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