multiple selection in the where clause

I need to do multiple selection in the where clause

select * 
  from BATS
  where REASON in
case when :P12_REASON = 'Rejects' then ('online', 'offline') else '' end
and
case when :P12_REASON = 'accepted' then ('online', 'offline', 'written') else '' end
and
goings on.....

Answer

You need to rewrite the clause using AND logic:

SELECT *
FROM BATS
WHERE (:P12_REASON = 'Rejects' AND REASON IN ('online', 'offline') OR
       :P12_REASON = 'accepted' AND REASON IN ('online', 'offline', 'written'))
  AND -- goings on...

Note the parentheses around this logic are necessary to avoid improper grouping with the logic following the AND.