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	Wed, 21 Apr 1999 17:45:34 -0400 (EDT)
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To: "Brett W. McCoy" <bmccoy@lan2wan.com>, pgsql-interfaces@postgreSQL.org
To: "Gene Selkov, Jr." <selkovjr@mcs.anl.gov>
Subject: Re: [INTERFACES] Detecting existance of table 
In-Reply-To: Your message of "Wed, 21 Apr 1999 19:00:20 EDT."
	<Pine.BSI.3.91.990421184714.10411U-100000@access1.lan2wan.com>
Date: Wed, 21 Apr 1999 16:45:16 -0400
From: "Gene Selkov Jr." <selkovjr@xnet.com>

> Is there a way of detecting the existance of a table via a function call? 

Not through the client library, as far as I can tell. Why would you
need a function call?  Send a query, like this one:

http://wit.mcs.anl.gov/EMP/list-classes.cgi?database=emp

> Actually, can an exception be caught somehow?  I'm 
> mainly doing this with PHP3, but I also need to do it via the Perl Pg.pm

That's easy in perl:

  eval {local $SIG{__DIE__}; do soemthing wrong here }

This piece of code will catch an exception caused by eval() and do
nothing.  Refer to the following document for an extensive discussion
of signal handling (__DIE__ is just a signal):

http://theory.uwinnipeg.ca/CPAN/data/pod2texi/perlipc.html

However, I don't see how anything you do in Pg might lead to an
exception (other than FPE). Queries against non-existent objects will
generate errors in the backend, of which your code will be notified
via Pg. But that will not cause any exceptions. You will just get
a different result code.

But I agree that filling your server log with harmless error messages
is not good. Query pg_class first.

--Gene