Finding the Median of a Value
You can use an SQL DataFlow to find the median of a value. You can do this in either a MySQL or Redshift DataFlow.
MySQL
Transform_data_1:
select * ,@row := @row + 1 as 'row count' from input_dataset, (select @row:=0) a order by `value`
Transform_data_2:
SELECT *, (CASE WHEN (SELECT MAX(`row count`) FROM transform_data_1) % 2 = 0 THEN ((SELECT `value` FROM transform_data_1 WHERE `row count` = (((SELECT MAX(`row count`) FROM transform_data_1)/2)+1)) + (SELECT `value` FROM transform_data_1 WHERE `row count` = (((SELECT MAX(`row count`) FROM transform_data_1)/2))) ) /2 WHEN (SELECT MAX(`row count`) FROM transform_data_1) % 2 != 0 THEN (SELECT `value` from transform_data_1 WHERE `row count` = (((SELECT MAX(`row count`) FROM transform_data_1)+1)/2) ) END) AS 'Median' FROM transform_data_1
Your output is then:
SELECT * FROM transform_data_2
Redshift
MEDIAN ( median_expression ) OVER ( [ PARTITION BY partition_expression ] )