PostgreSQL Tutorial: Boolean Data Type

Summary: in this tutorial, you will learn about the PostgreSQL Boolean data type and how to use it in designing the database tables.

Table of Contents

Introduction to the PostgreSQL Boolean type

PostgreSQL supports a single Boolean data type: BOOLEAN that can have three values: true, false and NULL.

PostgreSQL uses one byte for storing a boolean value in the database. The BOOLEAN can be abbreviated as BOOL.

In standard SQL, a Boolean value can be TRUE, FALSE, or NULL. However, PostgreSQL is quite flexible when dealing with TRUE and FALSE values.

The following table shows the valid literal values for TRUE and FALSE in PostgreSQL.

Note that the leading or trailing whitespace does not matter and all the constant values except for true and false must be enclosed in single quotes.

PostgreSQL Boolean examples

Let’s take a look at some examples of using the PostgreSQL Boolean data type.

First, create a new table stock_availability to log which products are available.

CREATE TABLE stock_availability (
   product_id INT PRIMARY KEY,
   available BOOLEAN NOT NULL
);

Second, insert some sample data into the stock_availability table. We use various literal value for the boolean values.

INSERT INTO stock_availability (product_id, available)
VALUES
	(100, TRUE),
	(200, FALSE),
	(300, 't'),
	(400, '1'),
	(500, 'y'),
	(600, 'yes'),
	(700, 'no'),
	(800, '0');

Third, use the following statement to check for the availability of products:

SELECT *
FROM stock_availability
WHERE available = 'yes';

 product_id | available
------------+-----------
        100 | t
        300 | t
        400 | t
        500 | t
        600 | t
(5 rows)

You can imply the true value by using the Boolean column without any operator. For example, the following query returns all products that are available:

SELECT *
FROM stock_availability
WHERE available;

Similarly, if you want to look for false values, you compare the value of the Boolean column against any valid Boolean constants.

The following query returns the products that are not available.

SELECT *
FROM stock_availability
WHERE available = 'no';

 product_id | available
------------+-----------
        200 | f
        700 | f
        800 | f
(3 rows)

Or you can use the NOT operator to check if values in the Boolean column are false like this:

SELECT *
FROM stock_availability
WHERE NOT available;

Set a default value of the Boolean column

To set a default value for an existing Boolean column, you use the SET DEFAULT clause in the ALTER TABLE statement.

For example, the following ALTER TABLE statement sets the default value for the available column in the stock_availability table:

ALTER TABLE stock_availability 
ALTER COLUMN available
SET DEFAULT FALSE;

If you insert a row without specifying the value for the available column, PostgreSQL uses FALSE:

INSERT INTO stock_availability (product_id)
VALUES (900);
SELECT *
FROM stock_availability
WHERE product_id = 900;

 product_id | available
------------+-----------
        900 | f
(1 row)

Likewise, if you want to set a default value for a Boolean column when you create a table, you use the DEFAULT constraint in the column definition as follows:

CREATE TABLE boolean_demo(
   ...
   is_ok BOOL DEFAULT 't'
);

In this tutorial, you have learned about the PostgreSQL BOOLEAN datatype and how to use it to store boolean data.

See more

PostgreSQL Tutorial: Data Types

PostgreSQL Documentation: Boolean Type