Simple way to calculate median with MySQL

Question

What\'s the simplest (and hopefully not too slow) way to calculate the median with MySQL? I\'ve used AVG(x) for finding the mean, but I\'m having a hard time fi

Answer 1

My solution presented below works in just one query without creation of table, variable or even sub-query. Plus, it allows you to get median for each group in group-by queries (this is what i needed !):

SELECT `columnA`, 
SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(`columnB` ORDER BY `columnB`), ',', CEILING((COUNT(`columnB`)/2))), ',', -1) medianOfColumnB
FROM `tableC`
-- some where clause if you want
GROUP BY `columnA`;

It works because of a smart use of group_concat and substring_index.

But, to allow big group_concat, you have to set group_concat_max_len to a higher value (1024 char by default). You can set it like that (for current sql session) :

SET SESSION group_concat_max_len = 10000; 
-- up to 4294967295 in 32-bits platform.

More infos for group_concat_max_len: https://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_group_concat_max_len