Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> Now the question: If the limit of one argument for DISTINCT aggs were
> removed (which I'm considering doing as part of an update to the
> aggregate ORDER BY patch I posted a while back), what should be the
> behaviour of agg(distinct x,y) where one or both of x or y is null?
> And should it depend on the strictness of the transition function?
I think you could probably just change it: make DISTINCT work as per
regular DISTINCT (treat null like a value, keep one copy). All the
spec-conforming aggregates are strict and would ignore the null in the
next step anyway.
regards, tom lane