Is there a better way to calculate the median (not average)

Question

Suppose I have the following table definition:

CREATE TABLE x (i serial primary key, value integer not null);

I want to calculate the MEDIAN o

Answer 1

Simple sql with native postgres functions only:

select 
    case count(*)%2
        when 1 then (array_agg(num order by num))[count(*)/2+1]
        else ((array_agg(num order by num))[count(*)/2]::double precision + (array_agg(num order by num))[count(*)/2+1])/2
    end as median
from unnest(array[5,17,83,27,28]) num;

Sure you can add coalesce() or something if you want to handle nulls.