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

Yes, with PostgreSQL 9.4, you can use the newly introduced inverse distribution function PERCENTILE_CONT(), an ordered-set aggregate function that is specified in the SQL standard as well.

WITH t(value) AS (
  SELECT 1   UNION ALL
  SELECT 2   UNION ALL
  SELECT 100 
)
SELECT
  percentile_cont(0.5) WITHIN GROUP (ORDER BY value)
FROM
  t;

This emulation of MEDIAN() via PERCENTILE_CONT() is also documented here.