-- check the query
SELECT *, UpdateMe = CASE WHEN a.SummaryType <> '0' THEN 'Y' ELSE 'N' END
FROM Table_A a
OUTER APPLY (
SELECT Result = (SUM(ai.Pass)/NULLIF(SUM(ai.VM_Id)*1.0,0)) * 100
FROM Table_A ai
WHERE ai.SummaryType <> '0'
AND ai.DeliveryDate = a.DeliveryDate
) x
-- check the query gain
SELECT *, UpdateMe = CASE WHEN a.SummaryType <> '0' THEN 'Y' ELSE 'N' END
FROM Table_A a
CROSS APPLY (
SELECT Result = (SUM(ai.Pass)/NULLIF(SUM(ai.VM_Id)*1.0,0)) * 100
FROM Table_A ai
WHERE ai.SummaryType <> '0'
AND ai.DeliveryDate = a.DeliveryDate
) x
WHERE a.SummaryType <> '0'
-- if it works, run the update
UPDATE a SET Perc = ISNULL(x.Result,0) -- do your rounding here
FROM Table_A a
CROSS APPLY (
SELECT Result = (SUM(ai.Pass)/NULLIF(SUM(ai.VM_Id)*1.0,0)) * 100
FROM Table_A ai
WHERE ai.SummaryType <> '0'
AND ai.DeliveryDate = a.DeliveryDate
) x
WHERE a.SummaryType <> '0'
SELECT * FROM Table_A
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden