Re: proposal: fix corner use case of variadic fuctions usage

Hello

so there is updated version

+ some lines of doc
+ new regress tests

there are no reply to my previous mail - so I choose

concat(variadic null) ---> NULL
concat(variadic '{}') ---> empty string

this behave should not be precedent for any other variadic "any"
function, because concat() and concat_ws() functions has a specific
behave - when it is called with one parameter returns string or empty
string

Regards

Pavel

2013/1/23 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
> 2013/1/23 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>>> next related example
>>
>>> CREATE OR REPLACE FUNCTION public.myleast(VARIADIC integer[])
>>> RETURNS integer
>>> LANGUAGE sql
>>> AS $function$
>>> select min(v) from unnest($1) g(v)
>>> $function$
>>
>> The reason you get a null from that is that (1) unnest() produces zero
>> rows out for either a null or empty-array input, and (2) min() over
>> zero rows produces NULL.
>>
>> In a lot of cases, it's not very sane for aggregates over no rows to
>> produce NULL; the best-known example is that SUM() produces NULL, when
>> anyone who'd not suffered brain-damage from sitting on the SQL committee
>> would have made it return zero. So I'm not very comfortable with
>> generalizing from this specific case to decide that NULL is the
>> universally right result.
>>
>
> I am testing some situation and there are no consistent idea - can we
> talk just only about functions concat and concat_ws?
>
> these functions are really specific - now we talk about corner use
> case and strongly PostgreSQL proprietary solution. So any solution
> should not too bad.
>
> Difference between all solution will by maximally +/- 4 simple rows
> per any function.
>
> Possibilities
>
> 1) A. concat(variadic NULL) => empty string, B. concat(variadic '{}')
> => empty string -- if we accept @A, then B is ok
> 2) A. concat(variadic NULL) => NULL, B. concat(variadic '{}') => NULL
> -- question - is @B valid ?
> 3) A. concat(variadic NULL) => NULL, B. concat(variadic '{}) => empty string
>
> There are no other possibility.
>
> I can live with any variant - probably we find any precedent to any
> variant in our code or in ANSI SQL.
>
> I like @2 as general concept for PostgreSQL variadic functions, but
> when we talk about concat() and concat_ws() @1 is valid too.
>
> Please, can somebody say his opinion early
>
> Regards
>
> Pavel
>
>
>
>> regards, tom lane