mysql - How to select standard deviation within a row? (in SQL - or R :)

Question

I wonder whether there is a way to select the standard deviation from several integer fields in MySQL within the same row. Obviously, if I use

SELECT STDDEV(col1) FROM mytable

I just get the standard deviation of that particular column. Let′s assume I have a table like: id,somefield1,somefield2, integerfield1,integerfield2,integerfield3, ... ,integerfield30 . Now I′d like to select the standard deviation of integerfield 1-30 within a row and save it AS sdfield . Of course I could use statistical software for this, but I just wonder if there is a way to do it directly in MySQL.

Answer 1

for simplicity, assume you have n columns, named A, B, C .... :

SELECT SQRT(  
  (A*A + B*B + C*C + ...)/n  - (A+B+C+...)*(A+B+C+...)/n/n) AS sd
  FROM table;