Question

I’m trying to perform calculations in T-SQL, but am having some problems with it.
Here is what I’m trying to do:

DECLARE @CNT money
SELECT @CNT = 0

Select Amount,
        case
            when Service like 'pay_in' then SET @CNT = @CNT + Amount
            when Service like 'pay_out' then SET @CNT= @CNT - Amount
        end
   from Payment where isActive = 1

select @CNT

Due to my poor knowledge of T-SQL syntax I’m stuck here, and would be very thankful if someone can push me in the right direction. Thank you!

Answer 1

SQL works best with set-based approaches. Try not to solve problems by iterating your data set, but rather by aggregating it.

DECLARE @CNT money

SELECT 
  @CNT = SUM(
    CASE Service 
      WHEN 'pay_in'  THEN Amount
      WHEN 'pay_out' THEN -1 * Amount
      ELSE 0
    END
  )
FROM
  Payment 
WHERE
  isActive = 1

SELECT @CNT