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Thread: Strict Set Returning Functions

Strict Set Returning Functions

From
Simon Riggs
Date:
STRICT functions return NULL if any of their inputs are NULL according
to the manual, so that they need not be executed at all.

Unless it is a Set Returning Function, in which case a NULL input is
not reduced nor does it to appear to be handled as a special case in
the executor function scan code.

So a function that is both STRICT and SET RETURNING will return rows.

Presumably this is just a case of missing documentation?

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Re: Strict Set Returning Functions

From
Tom Lane
Date:
Simon Riggs <simon@2ndQuadrant.com> writes:
> STRICT functions return NULL if any of their inputs are NULL according
> to the manual, so that they need not be executed at all.

> Unless it is a Set Returning Function, in which case a NULL input is
> not reduced nor does it to appear to be handled as a special case in
> the executor function scan code.

> So a function that is both STRICT and SET RETURNING will return rows.

Really?  The case behaves as expected for me.
        regards, tom lane

Re: Strict Set Returning Functions

From
Simon Riggs
Date:
On Wed, Jun 15, 2011 at 8:05 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
>> STRICT functions return NULL if any of their inputs are NULL according
>> to the manual, so that they need not be executed at all.
>
>> Unless it is a Set Returning Function, in which case a NULL input is
>> not reduced nor does it to appear to be handled as a special case in
>> the executor function scan code.
>
>> So a function that is both STRICT and SET RETURNING will return rows.
>
> Really?  The case behaves as expected for me.

Seems that's the wrong question. Let me return to why I raised this:

Why does evaluate_function() specifically avoid returning NULL for a
set returning function?
It could easily do the NULL test first, so it was applied to all
function types. That seems strange.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Re: Strict Set Returning Functions

From
Tom Lane
Date:
Simon Riggs <simon@2ndQuadrant.com> writes:
> On Wed, Jun 15, 2011 at 8:05 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Simon Riggs <simon@2ndQuadrant.com> writes:
>>> So a function that is both STRICT and SET RETURNING will return rows.

>> Really?  The case behaves as expected for me.

> Seems that's the wrong question. Let me return to why I raised this:

> Why does evaluate_function() specifically avoid returning NULL for a
> set returning function?

Because replacing the SRF call with a constant NULL would produce the
wrong result, ie, a single row containing NULL, not zero rows.
        regards, tom lane

Re: Strict Set Returning Functions

From
Simon Riggs
Date:
On Thu, Jun 16, 2011 at 12:24 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
>> On Wed, Jun 15, 2011 at 8:05 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Simon Riggs <simon@2ndQuadrant.com> writes:
>>>> So a function that is both STRICT and SET RETURNING will return rows.
>
>>> Really?  The case behaves as expected for me.
>
>> Seems that's the wrong question. Let me return to why I raised this:
>
>> Why does evaluate_function() specifically avoid returning NULL for a
>> set returning function?
>
> Because replacing the SRF call with a constant NULL would produce the
> wrong result, ie, a single row containing NULL, not zero rows.

OK, thanks.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services