This is classic database question to check candidates knowledge about SQL queries. You have a table where lets say you have duplicate entries (lets also say column1 and column2 can form a candidate key). Now you need to remove duplicates from then table. That is all rows in the table should be distinct. How would you do this?
Query to remove duplicate rows from table in Oracle
You can execute following query to remove duplicates -
DELETE FROM your_table WHERE rowid not in (SELECT MIN(rowid) FROM your_table GROUP BY column1, column2);