Select Records against all months of a given year form one table with records from second table - sql

Question

I have two tables in my database:
MembershipInstallments (ProjectId, AllotmentId, InstallmentId, EntryDate, AmountPaid)
Memberships (ProjectId, AllotmentId, ClientId, ClientName, RegistrationNo)
I want to select month wise payments made by a clients in a year. And also amount paid before the start of that year. My desired result set is
Let's say for the year 2019:
ClientName, RegistrationNumbers, PreviouslyPaidAmount (i.e. all amounts paid in 2018), AmountPaidInJuly 2019, AmountPaidInAugust2019. ..... AmountPaidIn Jun2020
where month is EntryDate from MembershipInstallments table.
I tried it like this, but it takes too long for large data set:
SELECT
ClientName, RegistrationNo,
(SELECT ISNULL(SUM(AmountPaid),0)
FROM MembershipInstallments
WHERE ProjectId = Membership.ProjectId
AND AllotmentId = Membership.AllotmentId
AND EntryDate < #fromDate) ASPreviouslyPaid,
(SELECT ISNULL(SUM(AmountPaid), 0)
FROM MembershipInstallments
WHERE ProjectId = Membership.ProjectId
AND AllotmentId = Memberhsip.AllotmentId
AND (MONTH(EntryDate) = 7) AND (YEAR(EntryDate) = YEAR(#fromDate)) AS JulyPayment
FROM
Memberships
WHERE
ProjectId = #projectId
Any help will be highly appreciated.

Answer 1

Scalar Subqueries tend to be badly optimized. In your case (same join-conditions) you can simply utilize conditional aggregation:
SELECT ms.ClientName,ms.RegistrationNo,
Sum(CASE WHEN mi.EntryDate<#fromDate THEN mi.AmountPaid ELSE 0 end) AS PreviouslyPaid,
Sum(CASE WHEN (Month(mi.EntryDate) = 7) AND (Year(mi.EntryDate) = Year(#fromDate)) THEN mi.AmountPaid ELSE 0)
FROM Memberships AS ms
LEFT JOIN MembershipInstallments AS mi -- don't know if Outer join is really needed
ON mi.ProjectId=ms.ProjectId
AND mi.AllotmentId=ms.AllotmentId
WHERE ms.ProjectId=#projectId
You might be able to do the aggregation before the join, i.e. in a CTE to further improve performance:
WITH cte AS
(
SELECT
ProjectId, AllotmentId,
Sum(CASE WHEN EntryDate<#fromDate THEN AmountPaid ELSE 0 END) AS PreviouslyPaid,
Sum(CASE WHEN (Month(EntryDate) = 7) AND (Year(EntryDate) = Year(#fromDate)) THEN AmountPaid ELSE 0 END) AS JulyPayment
FROM MembershipInstallments
WHERE ProjectId=#projectId
GROUP BY ProjectId, AllotmentId
)
SELECT ms.ClientName, ms.RegistrationNo, cte.PreviouslyPaid, cte.JulyPayment
FROM Memberships AS ms
JOIN cte
ON cte.ProjectId=ms.ProjectId
AND cte.AllotmentId=ms.AllotmentId
WHERE ms.ProjectId=#projectId
In both cases double-check if the result is correct (depends on the actual relation between those tables)