Ghislain Leveque - 5 months ago 36

SQL 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 of

`value`

Here is how I manage to calculate the MEDIAN but I guess there must be a better way:

`SELECT AVG(values_around_median) AS median`

FROM (

SELECT

DISTINCT(CASE WHEN FIRST_VALUE(above) OVER w2 THEN MIN(value) OVER w3 ELSE MAX(value) OVER w2 END)

AS values_around_median

FROM (

SELECT LAST_VALUE(value) OVER w AS value,

SUM(COUNT(*)) OVER w > (SELECT count(*)/2 FROM x) AS above

FROM x

GROUP BY value

WINDOW w AS (ORDER BY value)

ORDER BY value

) AS find_if_values_are_above_or_below_median

WINDOW w2 AS (PARTITION BY above ORDER BY value DESC),

w3 AS (PARTITION BY above ORDER BY value ASC)

) AS find_values_around_median

Any ideas?

Answer

Indeed there IS an easier way. In Postgres you can define your own aggregate functions. I posted functions to do median as well as mode and range to the PostgreSQL snippets library a while back.