Get Var() and AVG() from many columns - sql

Question

I'm building a query to show average and variance from many columns.
To get the average I use this:
SELECT *,
(SELECT AVG(t.c)
FROM (
SELECT peca_1 UNION ALL
SELECT peca_2 UNION ALL
SELECT peca_3 UNION ALL
SELECT peca_4 UNION ALL
SELECT peca_5 UNION ALL
SELECT peca_6 UNION ALL
SELECT peca_7 UNION ALL
SELECT peca_8 UNION ALL
SELECT peca_9 UNION ALL
SELECT peca_10
) t(c)
) as [media]
from Durabilidade
where cd_durabilidade = 1
The result is:
Now I need a new column with VAR(media) comparing each row with first row.
Any idea?

Answer 1

I think this is a case where cross apply is appropriate. I am assuming that you want the variance of the values as calculated by the var() function:
SELECT *, t.avgval as [media], t.varval
from Durabilidade d cross apply
(select avg(t.val) as avgval, var(t.val) as varval
from (select d.peca_1 union all
select d.peca_2 union all
select d.peca_3 union all
select d.peca_4 union all
select d.peca_5 union all
select d.peca_6 union all
select d.peca_7 union all
select d.peca_8 union all
select d.peca_9 union all
select d.peca_10
) t(val) -- t(val) to work
) t
where cd_durabilidade = 1

Answer 2

Something like this?
SELECT *,
VAR(media) AS [variance]
FROM
(
SELECT *,
(SELECT AVG(t.c)
FROM (
SELECT peca_1 UNION ALL
SELECT peca_2 UNION ALL
SELECT peca_3 UNION ALL
SELECT peca_4 UNION ALL
SELECT peca_5 UNION ALL
SELECT peca_6 UNION ALL
SELECT peca_7 UNION ALL
SELECT peca_8 UNION ALL
SELECT peca_9 UNION ALL
SELECT peca_10
) t(c)
) as [media]
from Durabilidade
where cd_durabilidade = 1
) x
GROUP BY
column1_from_durabilidade
,column2_from_durabilidade
--etc
,media