union query in sql 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: sql server union all example

SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions]
UNION ALL
SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions];

Example 3: sql union

Combines the results from 2 or more SELECT statements and returns only
distinct values.
Example: Returns the cities from the events and subscribers tables.
SELECT city FROM events
UNION
SELECT city from subscribers;