Result Not Showing When Using NOT IN in Query

Hi,

Result Not Shown in NOT IN Used Query.

The First Query Return 1 Row for the criteria

select * from RE_SURGERY_SCHEDULE where RSS_SURGERY_SCHEDULE_NUM='SG10131212/0003'


The Second Query Return 0 Row for the criteria

select * from WA_ADMISSION_TXN where WAT_SURGERY_SCHEDULE_NUM='SG10131212/0003'
Here I combine two queries but result not shown what is mistake in this query

select * from RE_SURGERY_SCHEDULE
where RSS_SURGERY_SCHEDULE_NUM not in (
select WAT_SURGERY_SCHEDULE_NUM from WA_ADMISSION_TXN)

---

Ragu Thangavel