Thread: Detecting existance of table

Is there a way of detecting the existance of a table via a function call?
I'm trying to implement a 'saved search' feature in a search engine, and
need to query a database to see if a particular table exists without
throwing an error.  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

Brett W. McCoy
                                         http://www.lan2wan.com/~bmccoy
-----------------------------------------------------------------------
Why is the alphabet in that order?  Is it because of that song?

> 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

Try this:
 select TRUE from pg_class where relname = 'my_table' and relkind = 'r';

José


"Brett W. McCoy" ha scritto:

> Is there a way of detecting the existance of a table via a function call?
> I'm trying to implement a 'saved search' feature in a search engine, and
> need to query a database to see if a particular table exists without
> throwing an error.  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
>
> Brett W. McCoy
>                                          http://www.lan2wan.com/~bmccoy
> -----------------------------------------------------------------------
> Why is the alphabet in that order?  Is it because of that song?