why union is used in sql query code example

Example 1: sql union

-- 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;

Example 2: union in sql

UNION:
COMBINES THE RESULT OF 2 QUERY AND
REMOVES DUPLICATE ROWS AND
SORTS BY FIRST COLUMN