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SQL Query Subtracting Values from Two Tables

I have two tables, demand and fte, that have department, shift and demand or fte. I need to calculate the need (demand – fte). What I get is a table with 9 entries. I’ve run into this before and for the life of me I cannot remember how I resolved it.

There is also a department table which I neglected. It only holds the departmentID & Name

Demand

department shift demand
A1 1 23
A1 2 26
A1 3 21

FTE

department shift fte
A1 1 26
A1 2 24
A1 3 18

Expected result:

department shift need
A1 1 -3
A1 2 2
A1 3 3

Current results:

department shift need
A1 1 -3
A1 2 0
A1 3 -5
A1 1 -1
A1 2 2
A1 3 -3
A1 1 5
A1 2 8
A1 3 3

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Answer

your join should be based on departmentid and shift :

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