First (aggregate)

-- Create a function that always returns the first non-NULL item
CREATE OR REPLACE FUNCTION public.first_agg ( anyelement, anyelement )
RETURNS anyelement AS $$
        SELECT $1;
$$ LANGUAGE SQL IMMUTABLE STRICT;
 
-- And then wrap an aggreagate around it
CREATE AGGREGATE public.first (
        sfunc    = public.first_agg,
        basetype = anyelement,
        stype    = anyelement
);