UNION Example The following statement combines the results of two queries with the UNION
operator, which eliminates duplicate selected rows. This statement shows that you must match datatype (using the TO_CHAR
function) when columns do not exist in one or the other table:
SELECT location_id, department_name "Department",
TO_CHAR(NULL) "Warehouse" FROM departments
UNION
SELECT location_id, TO_CHAR(NULL) "Department", warehouse_name
FROM warehouses;
UNION ALL Example The UNION
operator returns only distinct rows that appear in either result, while the UNION
ALL
operator returns all rows. The UNION
ALL
operator does not eliminate duplicate selected rows:
SELECT product_id FROM order_items
UNION
SELECT product_id FROM inventories;
SELECT location_id FROM locations
UNION ALL
SELECT location_id FROM departments;
A location_id
value that appears multiple times in either or both queries (such as '1700
') is returned only once by the UNION
operator, but multiple times by the UNION
ALL
operator.
INTERSECT Example The following statement combines the results with the
INTERSECT
operator, which returns only those rows returned by both queries:
SELECT product_id FROM inventories
INTERSECT
SELECT product_id FROM order_items;
MINUS Example The following statement combines results with the
MINUS
operator, which returns only unique rows returned by the first query but not by the second:
SELECT product_id FROM inventories
MINUS
SELECT product_id FROM order_items;