-- UNION: distinct values (slower)
SELECT emp_name AS name from employees
UNION
SELECT cust_name AS name from customers;
-- UNION ALL: keeps duplicates (faster)
SELECT emp_name AS name from employees
UNION ALL
SELECT cust_name AS name from customers;
union SQL
SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;