MySQL OR

Summary: In this chapter, we’ll learn how to use the MySQL OR operator to combine Boolean expressions for filtering data.

MySQL OR Operator

Introduction to the MySQL OR operator

The MySQL OR operators are used to filter records based on more than one condition and OR operator displays a record if either the first condition OR the second condition is true.

The following illustrates the syntax of the OR operator.

1	WHERE boolean_expression_1 OR boolean_expression_2

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

 Operator precedence

When we use more than one logical operator in a statement, MySQL evaluates the OR operators after the AND operators. This is called operator precedence.

The operator precedence determines the order of evaluation of the operators. MySQL evaluates the operator with the higher precedence first.

See the following example.

1	SELECT TRUE OR FALSE AND FALSE;

How it works

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

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

1	SELECT (TRUE OR FALSE) AND FALSE;

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

Let’s use the employees table in the sample database for the demonstration.

For example, To get only employees who is Software Engineer or Sales Rep. For this scenario we need to use the OR operator in the WHERE clause.

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SELECT  firstname, lastname, jobtitle, salary FROM  employees WHERE  jobtitle="Software Engineer" OR jobtitle="Sales Rep";

The following statement returns to get only those employees who is Software Engineer OR Sales Rep AND them salaries are more than 20000.

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SELECT  firstname, lastname, jobtitle, salary FROM  employees WHERE  (jobtitle="Software Engineer" OR jobtitle="Sales Rep")  AND salary > 20000;

In this chapter, we have learnt how to use the MySQL OR operator to combine Boolean expressions for filtering data.

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