Case stament use in where clause grive error

Question

i want to use this conditions but gives error. Please give me the solution of it
WHERE
CASE
WHEN CANCELLED_DATE IS NULL THEN
TO_DATE(INV_GL_DATE,'DD-MON-YY') <= TO_DATE (:P_DATE1,'DD-MON-YY')
ELSE
TO_DATE(INV_GL_DATE,'DD-MON-YY') >= TO_DATE(:P_DATE1,'DD-MON-YY')
END) --- <= TO_DATE(:P_DATE1,'DD-MON-YY')

Answer 1

Hi,
Remember that a CASE expression always evaluates to a single value in one of the SQL datatypes, such as VARCHAR2, NUMBER or DATE. (There is no Boolean datatype in SQL.)
You can't say
WHERE   CASE ... END;for the same reason that you can't say
WHERE   'Hello, world!';orWHERE   100;or
WHERE   SYSDATE;CASE expressions are really valuable because they allow you do perform IF-THEN-ELSE logic in places where you normally can't, like the SELECT clause.
The WHERE clause is a place where you can perform IF-THEN-ELSE logic anyway, so there's rarely a need for a CASE expression in a WHERE clause. It's just as efficient and just as clear (if not more so) to put all your conditions directly in the WHERE clause, like Max demonstrated.
Edited by: Frank Kulash on Feb 26, 2010 10:13 AM
user11995078 wrote:
Thanks Dear But how can we use with case and decodeWhy do you want to?
CASE does not help in this problem, any more than regular expressions or CONNECT BY or MODEL help. They are all great tools for particular jobs, but not for this job. Asking "How can I use CASE to do this?" Is like asking "How can I use a hammer to tighten a bolt?" Perhaps there is a way, but it's likely to be contrived and ridiculous.
Here's the least ridiculous way I can think of:
WHERE     ( TO_DATE (INV_GL_DATE, 'DD-MON-YY') 
     - TO_DATE (:P_DATE1,     'DD-MON-YY')
     ) * CASE
             WHEN  cancelled_date  IS NULL  THEN  1
                `                            ELSE -1
         END <= 0