Question

I have a table TableX. It contains three columns: A INT , B INT and C VARCHAR(1) (valid values for column C being the name of the columns ‘A’ or ‘B’). I need to count the number of occurrences where either of the following conditions are met:

1. When C is NULL and does contains values in either A or B greater than zero. or
2. When C is NOT NULL (i.e. ‘A’ or ‘B’) and the value in the specified column (A or B) is either zero or NULL.

My current stored procedure looks like

CREATE PROCEDURE ispcSomeName @NumOcc INT OUTPUT 
AS
SELECT COUNT(*) AS [NumOcc] 
FROM TableName 
WHERE (C IS NULL 
       AND ((A IS NOT NULL OR A > 0) OR 
            (B IS NOT NULL OR B > 0))) 
    OR (CritCarType IS NOT NULL 
        AND (CASE SET @TmpColumnName = CritCareType 
                 WHEN N'A' THEN (A IS NULL OR A <= 0) 
                 WHEN N'B' THEN (B IS NULL OR B <= 0)))
GO

The problem is that I need to check the column that C references. That is if C = 'A', I need to check if A IS NOT NULL OR A <= 0. There is clearly an issue with the SET in the final WHERE. I have got a few of these types of SPs to author and I want to avoid complex TSQL if I can help it…

How do I dynamically get reference to the relevant column in the WHERE clause?

Thanks for your time.

Answer 1

Select Count(*)
from tab
where 
(
    C is null and (Coalesce(A,0)>0 or Coalesce(B,0)>0)
)
or 
(
    C is not null and Case when C='A' then Coalesce(A,0) 
    when C='B' then Coalesce(B,0) end <=0
)