On Sun, Nov 20, 2016 at 2:45 AM, Pavel Stehule <pavel.steh...@gmail.com> wrote:
> > > 2016-11-19 22:12 GMT+01:00 Jeff Janes <jeff.ja...@gmail.com>: > >> I need "strict" MIN and MAX aggregate functions, meaning they return NULL >> upon any NULL input, and behave like the built-in aggregates if none of the >> input values are NULL. >> >> This doesn't seem like an outlandish thing to want, and I'm surprised I >> can't find other discussion of it. Perhaps because none of the words here >> are very effective as search terms as they are so individually common. >> >> I've hit upon a solution that works, but it is both ugly and slow (about >> 50 fold slower than the built-ins; for my current purpose this is not a big >> problem but I would love it to be faster if that could be done easily). >> >> So here is my approach. Any suggestions to improve it? Or are there >> better canned solutions I've failed to find? >> >> >> -- If no values have been delivered to the aggregate, the internal state >> is the >> -- NULL array. If a null values has been delivered, the internal status >> is an >> -- array with one element, which is NULL. Otherwise, it is an array with >> one element, >> -- the least/greatest seen so far. >> >> CREATE OR REPLACE FUNCTION strict_min_agg (anyarray,anyelement ) >> RETURNS anyarray LANGUAGE sql IMMUTABLE AS $$ >> SELECT CASE >> WHEN $1 IS NULL THEN ARRAY[$2] >> WHEN $1[1] IS NULL THEN $1 >> WHEN $2 IS NULL THEN ARRAY[$2] -- use $2 not NULL to preserve >> type >> ELSE ARRAY[least($1[1],$2)] END ; >> $$; >> >> >> CREATE OR REPLACE FUNCTION strict_min_final (anyarray) >> RETURNS anyelement LANGUAGE sql IMMUTABLE AS $$ >> SELECT CASE WHEN $1 IS NULL THEN NULL ELSE $1[1] END ; >> $$; >> >> CREATE AGGREGATE strict_min (x anyelement) ( >> sfunc = strict_min_agg, >> stype = anyarray, >> finalfunc = strict_min_final >> ); >> > > can you use plpgsql instead sql? > I can. Would there be an advantage? you can use composite type instead array too. > I tried a composite type of (flag int, value anyelement) but you can't use anyelement in a composite type. So the aggregate function couldn't be polymorphic. Or, that was my conclusion after making a few attempts. Maybe I need to give on polymorphism if I want to get performance? Cheers, Jeff
