Answer 1

Sorry Mani, but this is the reason why tables are design with IDs, cause there should be at least 1 unique value per entry, and SQL alone is not able to hold a row's value, compared it with another and eliminate the exact duplicate.

If Microsoft SQL Server you should be able to find easily and fast an answer looking at Transact SQL, if it's Oracle then look for PL-SQL solutions for this, there must be short scripts easy to modify to your needs. Good luck.