Question

Given two tables like this:

Date | Client | Category | Amount1 | x
A      B        C          234
X      Y        Z          456

MonthDate | Client | Category | Amount2 | y
B           C        D          567
A           B        C          123

How can I find records where x.Month(Date) = y.MonthDate, x.Client = y.Client, and x.Category = y.Category?

I need to be able to display Amount1 – Amount 2 = Net for certain clients.

Answer 1

A direct interpretation

SELECT x.Date, y.MonthDate, X.Client, Y.Category, X.Amount1 - Y.Amount2 Nett
FROM TBL1 X
JOIN TBL2 Y ON Month(x.Date) = y.MonthDate
           AND x.Client = y.Client
           AND x.Category = y.Category

However, if one of them is a monthly invoice and the other raw records, then you could be after an aggregate:

SELECT y.MonthDate, Y.Client, Y.Category, ISNULL(SUM(X.Amount1),0) - Y.Amount2 Nett
FROM TBL1 X
RIGHT JOIN TBL2 Y ON Month(x.Date) = y.MonthDate
           AND x.Client = y.Client
           AND x.Category = y.Category
GROUP BY y.MonthDate, Y.Client, Y.Category, Y.Amount2