On Wed, Jun 24, 2015 at 12:54 PM, Seb <splu...@gmail.com> wrote: > Hello, > > I've defined a function to calculate standard deviation of angular > values: > > CREATE AGGREGATE public.stddev(angle_vectors) ( > SFUNC=array_append, > STYPE=angle_vectors[], > FINALFUNC=angle_vectors_stddev_yamartino > ); > > The type angle_vectors is simply an array: > > CREATE TYPE public.angle_vectors AS > (x double precision, > y double precision); > COMMENT ON TYPE public.angle_vectors > IS 'This type holds the x (sine) and y (cosine) components of angle(s).'; > > How can I protect this function so that NULL is returned whenever *all* > input rows are NULL? > > Thanks for any feedback, >
Going from memory here... You don't "protect" anything. angle_vectors_stddev_yamartino needs to check whether its input array only contains null and, if so, return null. AFAIK there is no built-in way to check for only-null since "null = ALL(...)" doesn't work and you cannot say "IS NULL ALL(...)" In a simple case you could do something like: SELECT array_to_string(ARRAY[null,null]::integer[],'') = '' Not sure how that translates when using a composite type...and there is a difference between a non-null type with null components and a nulled type. David J.
