The UNION operator is used to combining the results of two tables, and it eliminates duplicate rows from the tables.

SELECT * FROM table1

UNION

SELECT * FROM table2;    

The MINUS operator is used to returning rows from the first query but not from the second query. The matching records of the first and second query and other rows from the first query will be displayed as a result set.

SELECT * FROM table1

MINUS

SELECT * FROM table2;

The INTERSECT operator is used to return rows returned by both the queries.

SELECT * FROM table1

INTERSECT

SELECT * FROM table2;