-- Error: A SELECT statement that assigns a value to a variable must not be combined with data-retrieval operations.
DECLARE @x SMALLINT
SELECT
AL1.Type,
AL3.Name,
AL3.Guid,
@x = (Sum (ISNULL(AL2."Quantity Added", 0)) - Sum (ISNULL(AL2."Quantity Taken",0)))
FROM dbo.Inv_Details AL1...