gistfile1.txt

create or replace function _final_median(anyarray)
    returns float8 as $$
with q as
(
    select val
    from unnest($1) val
    where VAL is not null
    order by 1
),
        cnt as
    (
        select COUNT(*) as c
        from q
    )
select AVG(val) :: float8
from
    (
        select val
        from q
        limit 2 - MOD((select c
                       from cnt), 2)
        offset GREATEST(CEIL((select c
                              from cnt) / 2.0) - 1, 0)
    ) q2;
$$ language sql immutable parallel safe;

drop aggregate if exists median (anyelement);
create aggregate median( anyelement ) (
    sfunc = array_append,
    stype = anyarray,
    finalfunc = _final_median,
    initcond = '{}',
    combinefunc = array_cat,
    parallel = safe
);