From: Tom Lane <tgl@sss.pgh.pa.us>
To: srn@coolheads.com
cc: pgsql-docs@postgresql.org
Subject: Re: can't be both non-capturing and still capture
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Comments: In-reply-to srn@coolheads.com
	message dated "Mon, 03 Jul 2017 20:47:55 -0000"
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Date: Mon, 03 Jul 2017 22:10:03 -0400
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srn@coolheads.com writes:
> Here, the whole regexp is non-capturing, right, so how can the result be
> reported as shown?

No, the outer parens are non-capturing, but the ones inside them still
are capturing parens.

Perhaps it would clarify matters if you tried it with plain outer parens:

=# SELECT regexp_matches('abc01234xyz', '((.*?)(\d+)(.*)){1,1}');
       regexp_matches        
-----------------------------
 {abc01234xyz,abc,01234,xyz}
(1 row)

In this case we get a report from each of the four sets of capturing
parens.  Or another example:

=# SELECT regexp_matches('abc01234xyz', '((?:.*?)(\d+)(.*)){1,1}');
     regexp_matches      
-------------------------
 {abc01234xyz,01234,xyz}
(1 row)

Outer parens capture, first inner set don't, other two inner sets do.

			regards, tom lane


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