If the columns and relative data types in the source tables are the same, the set operator allows the user to retrieve data from two or more tables at once.  Except for duplicate entries, the UNION operator returns all rows from both tables.  UNION ALL- it returns all the rows from both the tables along with the duplicate rows.  MINUS- it retrieves rows from the first table that are not present in the second.  INTERSECT – it returns just the rows that are shared by both tables.