When I try to create a unique index on a large table, I get a unique contraint error. The unique index in this case is a composite key of 4 columns. Is there an efficient way to identify the duplicates other than : select col1, col2, col3, col4, count() from Table1 group by col1, col2, col3, col4 having count() 1 The explain plan above shows full table scan with extremely high cost, and just want to find if there is another way. Thanks !