How to use STDEV over() in SQL Server 2017 Express? - sql-server-express

Question

I am trying to get the STDEV of MCW_NM column but I want it to be STDEV of all rows not per group by BLADEID. But in Variance_Blade_MCW I need it to be grouped by BLADEID. I have tried over() but I get this error:
Column 'ENG.DBO.MCW_BCL_WEDGE.MCW_NM' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
Can anyone help me? Below is my query.
PS: I am having difficulty explaining the problem so please bear with me. Let me know if you have clarifications! thanks a lot!
SELECT
BladeID,
Total_Sigma_MCW = STDEV(MCW_NM) OVER (),
CountD_Blade = COUNT(BLADEID) OVER (),
Variance_Blade_MCW = SQUARE(STDEV(MCW_NM))
FROM
ENG.DBO.MCW_BCL_WEDGE
WHERE
TESTDATE > GETDATE() - 6
GROUP BY
BLADEID
HAVING
COUNT(BladeID) >= 5000

Answer 1

I don't have access to mssql at the moment, but this might work. The inner query returns 1 row per BladeID with what I think are the aggregates you want. Problem is window functions always return 1 row for each row in the source, so the outer query flattens this.
SELECT DISTINCT
BladeID,
Total_Sigma_MCW = STDEV(MCW_NM) OVER (PARTITION BY 1),
Variance_Blade_MCW,
CountD_Blade,
FROM
(
SELECT
BladeID,
MCW_NM,
CountD_Blade = COUNT() OVER (PARTITION BY BladeID),
Variance_Blade_MCW = SQUARE(STDEV(MCW_NM) OVER (PARTITION BY BLADEID))
FROM
ENG.DBO.MCW_BCL_WEDGE
WHERE
TESTDATE > GETDATE() - 6
) q
WHERE CountD_Blade >= 5000
It may be more efficient to create two queries, one to group by BladeID and one over the full dataset and join them.