OR operator in SQL

The OR operator in SQL is used to combine multiple conditions in a WHERE clause, but unlike the AND operator, it only requires one of the conditions to be true for a row to be included in the result set. This makes the OR operator particularly useful for filtering data based on alternative criteria, allowing for more flexible and inclusive queries.

The OR operator comes from a math area called Boolean algebra, that operates with TRUE or FALSE values. Think of OR as making a choice between two things: if either one is true, or both are, then the whole thing is true. It’s really useful in SQL because it helps you build more flexible conditions for filtering data.

OR application in SQL

The truth table (a tool used in boolean algebra to show operotor’s output for all possible inputs) for the OR operator looks like this:

A	B	A OR B
TRUE	TRUE	TRUE
TRUE	FALSE	TRUE
FALSE	TRUE	TRUE
FALSE	FALSE	FALSE

This table shows that the OR operator returns true when any value of A or B is true, mirroring its use in SQL where a row must satisfy at least one condition connected by the OR operator to be included in the result set.

Thus, the OR operator in SQL is a direct application of mathematical principles from boolean algebra, enabling flexible filtering of data based on multiple criteria.

When using the OR operator, at least one condition must be true for the rows to be included in the result set. It helps greatly with filtering data based on multiple criteria.

OR in WHERE clause

The WHERE clause is where the OR operator is most commonly used, enabling the selection of rows that match any one of the provided conditions. For instance, here’s a query that lists all users that are 21-65 years old:

SELECT *
FROM books
WHERE
  genre = 'Thriller'
  OR genre = 'Horror'

Using OR in SELECT clause

Although the OR operator is predominantly used within WHERE clauses to filter selected data based on conditions, its principle of inclusivity can indirectly influence how SELECT statements are constructed.

Here’s an example of such a query:

SELECT
  genre = 'Thriller' OR genre = 'Horror' AS is_scary_book,
  *
FROM books

Tips for using OR in SQL

Remember that if any condition connected by OR for a row is true, this row will be included in the result set
Use parentheses () to group conditions and control the precedence of evaluation, especially when combining AND with OR operators.