在WHERE子句中添加CASE WHEN

Question

I used the following WHERE clause

WHERE (TYPE1 = :P3_ITEM1 OR :P3_ITEM1 IS NULL)

to filter my query on TYPE1 and it worked fine to display the records of same TYPE1 when page item P3_ITEM1 is not null.

Now I need to add two more filters for TYPE2 and TYPE3. Normally only one page item P3_ITEM1, P3_ITEM2, or P3_ITEM3 is not null, so I need to filter on whichever on is not null.

I tried

WHERE (TYPE1=:P3_ITEM1 OR :P3_ITEM1 IS NULL) OR
  (TYPE2=:P3_ITEM2 OR :P3_ITEM2 IS NULL) OR
  (TYPE3=:P3_ITEM3 OR :P3_ITEM3 IS NULL) 

but it did not work.

I tried using CASE statement in my WHERE clause but no success so far. Can anyone help?

WHERE CASE
WHEN (:P3_ITEM1 IS NOT NULL) THEN (TYPE1=:P3_ITEM1)
WHEN (:P3_ITEM2 IS NOT NULL) THEN (TYPE2=:P3_ITEM2)
WHEN (:P3_ITEM3 IS NOT NULL) THEN (TYPE3=:P3_ITEM3)

Answer 1

You can simply use AND to combine the various filters. Each filter will evaluate to true if the parameter for it is NULL , so if all three are NULL you will get all records, but you can fill in a any, or even all three parameters to filter out unwanted records.

WHERE
  (TYPE1 = :P3_ITEM1 OR :P3_ITEM1 IS NULL) AND
  (TYPE2 = :P3_ITEM2 OR :P3_ITEM2 IS NULL) AND
  (TYPE3 = :P3_ITEM3 OR :P3_ITEM3 IS NULL)