Question

I have a table like:

id    B       C
a     0.5     10.1
b     0.6     2.3
c     0.9     2.1
d     15.2    8.2

And I would like to calculate a quantity like: “the standard deviation of the C for which B is below the average”.

And I don’t know how to do that.

select ssdev_pop(C) from (select B, C from table where B < avg(B) );

Doesn’t work, and I don’t know how to access to avg(B) in one go (I know I could calculate it and plug it into a second query but I want to avoid that).

Can somebody help?

Answer 1

try this one,

SELECT stddev_pop(C) 
FROM
(
   SELECT B, C
   FROM   table1
   WHERE  B < (SELECT AVG(B) FROM table1 )
) s

Demo: http://www.sqlfiddle.com/#!2/9d570/8