PL/SQL block to sql case

Question

Hello,
I have a newbie sql question:
I have the following pl/sql block that I want to transform in sql case code:
             IF Num_WholesaleNonDiscountValue > 0.0 THEN
                  UsageStatus := 'CHARGE';
                  if Num_WholesaleNonDiscountValue < 1.0 then
                      WholesaleNonDiscountValue := '0' || TO_CHAR(Num_WholesaleNonDiscountValue);
                    else
                      WholesaleNonDiscountValue := TO_CHAR(Num_WholesaleNonDiscountValue);
                  end if;
              ELSE
                  UsageStatus := 'FREE';
                  WholesaleNonDiscountValue := TO_CHAR(Num_WholesaleNonDiscountValue);
              END IF;All I do is the following code:
select (case when Num_WholesaleNonDiscountValue > 0.0 then
                          (case Num_WholesaleNonDiscountValue < 1.0 then  '0' || TO_CHAR(Num_WholesaleNonDiscountValue
                           else TO_CHAR(Num_WholesaleNonDiscountValue))
         else TO_CHAR(Num_WholesaleNonDiscountValue)) from table_name;I do not know how to evaluate the UsageStatus variable, where to put it in the select statement.
This is for my learning process.
Thanks in advanced,
Dan
Edited by: danut68 on Jan 13, 2010 5:52 AM

Answer 1

Hi, Dan,
I think you want something like this:
SELECT     CASE
          WHEN  Num_WholesaleNonDiscountValue > 0
          THEN  'CHARGE'
          ELSE  'FREE'
     END                              AS UsageStatus
,     CASE
          WHEN  Num_WholesaleNonDiscountValue > 0
          AND   Num_WholesaleNonDiscountValue < 1
          THEN  '0'
     END || TO_CHAR (Num_WholesaleNonDiscountValue)     AS WholesaleNonDiscountValue
FROM     table_x
;A CASE expression returns one value.
In PL/SQL, you can do two or more completely separate things (set two different variables, for example) in the same IF-THEN-ELSE block.
To get the same results in SQL requires a completely different approach.
The clearest is to use a different CASE expression for each of the things you're trying to do, as I did above. The WHEN clauses of those CASE statements may be very similar, even identical.
Sometimes you can factor out some of the logic (using a sub-query, perhaps) so that the logic that has to be repeated in each CASE expression is very simple.
Another option for setting two variables is to have a single CASE expression that returns a string wihich is the concatenation of two different varibales, which you later parse into two separate variables. I would do this only as a last resort.