Re: Declaring a strict function returns not null / eval speed

Moin,

On 2019-10-20 16:27, Tom Lane wrote:
> Tels <nospam-pg-abuse@bloodgate.com> writes:
>> On 2019-10-20 13:30, Andreas Karlsson wrote:
>>> Agreed, this sounds like something useful to do since virtually all
>>> strict functions cannot return NULL, especially the ones which are
>>> used in tight loops. The main design issue seems to be to think up a
>>> name for this new level of strictness which is not too confusing for
>>> end users.
> 
>> STRICT NONULL? That way you could do
> 
>>    CREATE FUNCTION f1 ... STRICT;
>>    CREATE FUNCTION f2 ... STRICT NONULL;
>>    CREATE FUNCTION f3 ... NONULL;
> 
>> and the last wold throw "not implementet yet"? "NEVER RETURNS NULL"
>> would also ryme with the existing "RETURNS NULL ON NULL INPUT", but I
>> find the verbosity too high.
> 
> "RETURNS NOT NULL", perhaps?  That'd have the advantage of not 
> requiring
> any new keyword.

Hm, yes, that would be a good compromise on verbosity and align even 
better the other "RETURNS ..." variants.

> I'm a little bit skeptical of the actual value of adding this 
> additional
> level of complexity, but I suppose we can't determine that reliably
> without doing most of the work :-(

Maybe it would be possible to simulate the effect somehow? Or at least 
we could try to find practical queries where the additional information 
results in a much better plan if RETRUNS NOT NULL was set.

Best regards,

Tels