MySQL OR Operator

 MySQL OR Operator

Summary: in this tutorial, you will learn how to use the MySQL OR operator to combine Boolean expressions for filtering data.

Introduction to the MySQL OR operator

The MySQL OR operator combines two Boolean expressions and returns true when either condition is true.

The following illustrates the syntax of the OR operator.

boolean_expression_1 OR boolean_expression_2

Both boolean_expression_1 and boolean_expression_2 are Boolean expressions that return true, false, or NULL.

The following table shows the result of the OR operator.

	TRUE	FALSE	NULL
TRUE	TRUE	TRUE	TRUE
FALSE	TRUE	FALSE	NULL
NULL	TRUE	NULL	NULL

MySQL OR short-circuit evaluation

MySQL uses short-circuit evaluation for the OR operator. In other words, MySQL stops evaluating the remaining parts of the statement when it can determine the result.

See the following example.

SELECT 1 = 1 OR 1 / 0;

1 = 1 OR 1 / 0
--------------
1

Because the expression 1 = 1 always returns true, MySQL does not evaluate the 1 / 0. If it did, it would issue an error because of the division by zero error.

Operator precedence

When you use more than one logical operator in an expression, MySQL always evaluates the OR operators after the AND operators. This is called operator precedence which determines the order of evaluation of the operators. MySQL evaluates the operator with higher precedence first.

See the following example.

SELECT true OR false AND false;

true OR false AND false
-----------------------
1

How it works

1. First, MySQL evaluates the AND operator, therefore the expression false AND false returns false.
2. Second, MySQL evaluates the OR operator hence the expression true OR false returns true.

To change the order of evaluation, you use the parentheses, for example:

SELECT (true OR false) AND false;

(true OR false) AND false
-------------------------
0

How it works

1. First, MySQL evaluates the expression in the parenthesis (true OR false) returns true
2. Second, MySQL evaluates the remaining part of the statement, true AND false returns false.

MySQL OR operator examples

We’ll use the  customers table from the sample database for the demonstration.

For example, to get the customers who locate in the USA or France, you use the OR operator in the WHERE clause as follows:

SELECT    
	customername, 
	country
FROM    
	customers
WHERE country = 'USA' OR 
      country = 'France';

As you can see from the result, the query returns customers who locate in the USA or France.

The following statement returns the customers who locate in the USA or France and have a credit limit greater than 100,000.

SELECT   
	customername, 
	country, 
	creditLimit
FROM   
	customers
WHERE(country = 'USA'
		OR country = 'France')
	  AND creditlimit > 100000;

Notice that if you do not use the parentheses, the query will return the customers who locate in the USA or the customers located in France with a credit limit greater than 10,000.

SELECT    
	customername, 
	country, 
	creditLimit
FROM    
	customers
WHERE country = 'USA'
		OR country = 'France'
		AND creditlimit > 10000;

In this tutorial, you have learned how to use the MySQL OR operator to combine Boolean expressions for filtering data.