How to calculate the median value in Postgresql without using window function? - postgresql

Question

I have a table like this:
Now I have this code that can get the median value:
SELECT ROUND((t.middle1 + b.middle2) / 2, 2) AS median_item_count
FROM (
SELECT MAX(item_count) AS middle1
FROM (
SELECT item_count,
COUNT(*) OVER() AS row_count,
ROW_NUMBER() OVER (ORDER BY item_count) AS row_number
FROM orders
WHERE item_count <> 0
) top
WHERE (row_number::float / row_count) <= 0.50
) t,
(
SELECT MIN(item_count) AS middle2
FROM (
SELECT item_count,
COUNT(*) OVER() AS row_count,
ROW_NUMBER() OVER (ORDER BY item_count DESC) AS row_number
FROM orders
WHERE item_count <> 0
) bottom
WHERE (row_number::float / row_count) <= 0.50
) b
;
How can I get the median value without using window function OVER()and without using the percentile_disc function???

Answer 1

You can use this function which calculates the median of numeric array elements:
create or replace function median(numeric[])
returns numeric language sql immutable as
$$
select avg(val)
from (
select val
from unnest($1) val
order by 1
limit 2 - mod(array_upper($1, 1), 2)
offset ceil(array_upper($1, 1) / 2.0) - 1
) sub;
$$;
select median(array_agg(item_count))
from orders;