Question

I have a T-SQL query where I want all negative quantities to be zeroed out.

SELECT 
p.productnumber, 
v.[Description],
SUM(i.Quantity) as quantity
FROM ...
LEFT JOIN ...
LEFT JOIN ...
LEFT JOIN ...
GROUP BY productnumber, [Description]

Basically if the sum is made up of 5, 5, -1, the result should be 5+5+0=10, and not (5+5+(-1)=9.

How would I do that?

Answer 1

You could use a CASE statement

SUM(CASE WHEN i.Quantity < 0 THEN 0 ELSE i.Quantity END)

Or the proprietary IIF version

IIF(i.Quantity < 0, 0, i.Quantity)

Or a more obscure version

SUM(NULLIF(i.Quantity, -ABS(i.Quantity)))

or just exclude these rows altogether in the WHERE clause if they are not needed for any other purpose.

In Azure SQL Database you can now also use the GREATEST function for this

GREATEST(i.Quantity,0)