How to use the CASE Expression in Where Cluase?

Question

Hi All,
I'm trying to use the CASE Expression in the Where Clause at some trigger on the Form?
I've tried this Code:
Declare
N Number;
begin
SELECT COUNT(E.EMP_SID)
     INTO N
     FROM EMPLOYEES E, RANKS R
     WHERE CASE WHEN R.qualification_sid = 1104 AND E.rank_sid = 8 THEN
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.spe_per)+1)
     ELSE
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.mili_yea_per)+1)
     END
     BETWEEN TO_DATE('01-07-2011', 'DD-MM-RR') AND TO_DATE('31-07-2011', 'DD-MM-RR');
END;
When I run this code as a normal query at any SQL editor it works successfully, But When I Compile it at some trigger on the Form it gives me this error:
Encountered the symbol "CASE" when expecting one of the following:
( - + mod ......
Heeey how to specify the previous code to be shown as code in the thread?
Note: I'm using Forms 6i

Answer 1

OK I tried it and worked but for one condition:
WHERE DECODE (E.qualification_sid, 1104,
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.spe_per)+1),
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.mili_yea_per)+1))
     BETWEEN TO_DATE('01-07-2011', 'DD-MM-RR') AND TO_DATE('31-07-2011', 'DD-MM-RR')
But how to put two conditions for the same Expression:
WHERE DECODE ((E.qualification_sid, 1104) AND (E.RANK_SID, 8),
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.spe_per)+1),
     (TO_DATE(E.RANK_DATE, 'DD-MM-RR')+(365*M.mili_yea_per)+1))
     BETWEEN TO_DATE('01-07-2011', 'DD-MM-RR') AND TO_DATE('31-07-2011', 'DD-MM-RR')
The previous code gives me this error: missing right parenthesis