Sub Query selection based on parameter value selected

Question

I have a parameter, and based on the value selected, I want to run one of two queries. I thought I could do either an IF THEN ELSE, or a CASE, but neither seem to be working.
What I'm trying to do is this:
IF parameter_value = 338 THEN
(RUN THIS SELECT QUERY)
ELSE
(RUN THIS SELECT QUERY)
END IF
or
SELECT CASE WHEN parameter_value = 338 THEN (RUN THIS SELECT QUERY)
ELSE (RUN THIS SELECT QUERY)
END X
I'm getting errors with both. For the CASE statement, it says "too many values". For the IF statement, it just says "invalid SQL statement".
Any suggestions would be appreciated.
Thanks.

Answer 1

Looks like this is what you want
SQL> WITH T
  2       AS (SELECT LEVEL col
  3             FROM DUAL
  4           CONNECT BY LEVEL <= 5)
  5  SELECT *
  6    FROM T;
       COL
         1
         2
         3
         4
         5
SQL>
SQL> VARIABLE parameter_value    NUMBER
SQL> EXEC    :parameter_value := 338;
PL/SQL procedure successfully completed.
SQL>
SQL> WITH T
  2       AS (SELECT LEVEL col
  3             FROM DUAL
  4           CONNECT BY LEVEL <= 5)
  5  SELECT col
  6    FROM T
  7   WHERE col = DECODE (:parameter_value, 338, col, :parameter_value);  --- If 338 then select all if not 338 select only the one with parameter_value.
       COL
         1
         2
         3
         4
         5
SQL>
SQL> EXEC :parameter_value := 2;
PL/SQL procedure successfully completed.
SQL>
SQL> WITH T
  2       AS (SELECT LEVEL col
  3             FROM DUAL
  4           CONNECT BY LEVEL <= 5)
  5  SELECT col
  6    FROM T
  7   WHERE col = DECODE (:parameter_value, 338, col, :parameter_value);
       COL
         2
SQL>
SQL> EXEC :parameter_value := 3;
PL/SQL procedure successfully completed.
SQL>
SQL> WITH T
  2       AS (SELECT LEVEL col
  3             FROM DUAL
  4           CONNECT BY LEVEL <= 5)
  5  SELECT col
  6    FROM T
  7   WHERE col = DECODE (:parameter_value, 338, col, :parameter_value);
       COL
         3
SQL> You need to use following where clause in your query
WHERE column_name = DECODE (parameter_value, 338, col, parameter_value); -- replace the column_name with name of the column you are comparing against.G.
Edited by: G. on Mar 8, 2011 3:36 PM
formatted and added comments