Re: unique names in variables and columns in plsql functions

On Mon, Mar 27, 2006 at 10:02:24AM -0500, Tom Lane wrote:
> Wiebe Cazemier <halfgaar@gmail.com> writes:
> > DECLARE
> >   provider_id INTEGER;
> > BEGIN
> >   provider_id := (SELECT provider_id FROM investment_products WHERE id =
> > my_new.investment_product_id);
> > END;
> 
> > After a lot of trouble, I found out this line doesn't work correctly
> > with the variable name as it is. It doesn't give an error or anything,
> > it just retrieves some wrong value (probably NULL).
> 
> It'll retrieve whatever the current value of the plpgsql variable
> provider_id is.  plpgsql always assumes that ambiguous names refer
> to its variables (indeed, it isn't even directly aware that there's
> any possible ambiguity here).
> 
> > I was somewhat surprised to discover this. Can't Postgres determine that
> > the provider_id in the SELECT statement is not the same one as the variable?
> 
> How and why would it determine that?  In general it's perfectly normal
> to use plpgsql variable values in SQL commands.  I don't think it'd make
> the system more usable if the parser tried to apply a heuristic rule
> about some occurrences being meant as variable references and other ones
> not.  If the rule ever got it wrong, it'd be even more confusing.

BTW, I believe SELECT investment_products.provider_id would work here,
but I'm too lazy to test that theory out.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461