Decode for EXISTS and NOT EXISTS conditions

Question

Hello all,
I need to use either EXISTS or NOT EXISTS before the subquery based on the situation. I have written a test query but its erroring out. Please check it.
select 1 from dual
where DECODE('A','A',EXISTS ,NOT EXISTS)
(select ename from EMP
where ename = 'SCOTT')
Thank You
KK

Answer 1

DECODE will not replace part of the query. Functions don't work that way.
(It won't work if you put EXISTS and NOT EXISTS in quotes, either.)
What you want is something like
WHERE (<condition> AND EXISTS...) OR (<not-condition> AND NOT EXISTS...)You can also do:
SELECT 1
FROM dual
CROSS JOIN (SELECT COUNT(1) AS exists_fg FROM emp WHERE ename = 'SCOTT') ex
WHERE (<condition> AND exists_flag > 0) OR (<not-condition> AND exists_flag = 0)This way, you don't have to include the entire WHERE EXISTS condition twice.
-- Don