Still i have few concern on your clarification .
1) Your assumption unique no column does not have clustered index . The unique column is common column between both (Working table) and (History Table).We are using "unique no" column as common connector for both the tables .
2) My Requirement is to compare the UNIQUE column exist in working table is available in History table or not . Working table data will have always fresh set of data. If unique no exists I will update the "TARGET TABLE " modeflag column as updated record.
In this scenario still you prefer left outer join or inner join . Your valuable suggestion are welcome.
I appreciate the quick response on the above query .
Thanks once again.