Намерих решение в PostgreSQL, използвайки PL/Python.
Въпреки това оставям въпроса отворен, в случай че някой друг излезе с решение в mySQL.
CREATE TYPE boxplot_values AS (
min numeric,
q1 numeric,
median numeric,
q3 numeric,
max numeric
);
CREATE OR REPLACE FUNCTION _final_boxplot(strarr numeric[])
RETURNS boxplot_values AS
$$
x = strarr.replace("{","[").replace("}","]")
a = eval(str(x))
a.sort()
i = len(a)
return ( a[0], a[i/4], a[i/2], a[i*3/4], a[-1] )
$$
LANGUAGE 'plpythonu' IMMUTABLE;
CREATE AGGREGATE boxplot(numeric) (
SFUNC=array_append,
STYPE=numeric[],
FINALFUNC=_final_boxplot,
INITCOND='{}'
);
Пример:
SELECT customer_id as cid, (boxplot(price)).*
FROM orders
GROUP BY customer_id;
cid | min | q1 | median | q3 | max
-------+---------+---------+---------+---------+---------
1001 | 7.40209 | 7.80031 | 7.9551 | 7.99059 | 7.99903
1002 | 3.44229 | 4.38172 | 4.72498 | 5.25214 | 5.98736
Източник:http://www.christian-rossow.de/articles/PostgreSQL_ngplogplotfunction