Re: A question about PL/pgSQL DECLAREd variable behavior

On Thu, Oct 22, 2015 at 6:54 PM, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com
> wrote:

> On Fri, Oct 23, 2015 at 10:27 AM, Dane Foster <studdugie(at)gmail(dot)com> wrote:
> > On Thu, Oct 22, 2015 at 2:00 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>
> wrote:
> >> On 10/21/15 9:32 PM, Dane Foster wrote:
> >>>
> >>> "If STRICT is not specified in the INTO clause, then target will be
> >>> set to the first row returned by the query, or to nulls if the
> query
> >>> returned no rows."
> >>>
> >>> Foot removed from mouth.
> >>
> >> Note however that there's some unexpected things when checking whether a
> >> record variable IS (NOT) NULL. It's not as simple as 'has the variable
> been
> >> set or not'.
> >
> > Please elaborate. I'm entirely new to PL/pgSQL so the more details you
> can
> > provide the better.
> > Thanks,
>
> The surprising thing here, required by the standard, is that this
> expression is true:
>
> ROW(NULL, NULL) IS NULL
>
> So "r IS NULL" is not a totally reliable way to check if your row
> variable was set or not by the SELECT INTO, if there is any chance
> that r is a record full of NULL. "r IS NOT DISTINCT FROM NULL" would
> work though, because it's only IS [NOT] NULL that has that strange
> special case. Other constructs that have special behaviour for NULL
> don't consider a composite type composed of NULLs to be NULL. For
> example IS DISTINCT FROM, COALESCE, COUNT, STRICT functions.
>
> --
> Thomas Munro
> http://www.enterprisedb.com
>
​
Someone should include your explanation in the [fine] manual.

Dane​