Re: Adding XMLEXISTS to the grammar

From: Mike Fowler <mike(at)mlfowler(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Adding XMLEXISTS to the grammar
Date: 2010-06-22 17:17:46
Message-ID: 4C20F03A.5010001@mlfowler.com
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> Look at how the POSITION() pseudofunction is defined around gram.y
> line 9651. Essentially any special syntax of this type gets converted
> to a regular function call internally. So in your case I think there
> will be some function that gets called something ike this:
>
> xmlexists(xpath_expression, xml_expression)
>
> ...but the grammar can be modified to allow a different syntax for
> that function call.
>
I've finally managed to get gram.y to parse the syntax correctly. After
progressing from a segmentation fault that occured when the grammar was
correct I'm now left with a cryptic error:

xmltest=# SELECT COUNT(id) FROM xmltest WHERE xmlexists('/menu/beers'
PASSING BY REF data);
ERROR: unrecognized node type: 1852140847

At a guess there is another step that I need to do after modifying
gram.y. One mailing list posting I found mentioned copyfuncs.c but
really I'm unsure as to what next. Anyone know what the missing step is?

Regards,

--
Mike Fowler
Registered Linux user: 379787

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