AND Operator

Introduction to the PostgreSQL AND operator

The AND operator is a logical operator that combines two boolean expressions. A boolean expression in PostgreSQL evaluates to one of three values: TRUE, FALSE, or NULL.

Basic syntax:

expression1 AND expression2

The truth table for AND:

• TRUE AND TRUE → TRUE
• TRUE AND FALSE → FALSE
• TRUE AND NULL → NULL
• FALSE AND FALSE → FALSE
• FALSE AND NULL → FALSE (because one side is definitively false)
• NULL AND NULL → NULL

The key rule: AND returns TRUE only when both expressions are true. If either is definitively FALSE, the result is FALSE regardless of the other side.

Basic AND examples

SELECT true AND true   AS result;  -- t
SELECT true AND false  AS result;  -- f
SELECT true AND null   AS result;  -- null
SELECT false AND null  AS result;  -- f
SELECT null AND null   AS result;  -- null

Using AND in a WHERE clause

The most common use of AND is combining multiple filter conditions in a WHERE clause. All conditions joined by AND must be true for a row to be included in the result.

This query finds films from the DVD rental database that are longer than 180 minutes and have a rental rate below $1.00:

SELECT title, length, rental_rate
FROM film
WHERE length > 180
  AND rental_rate < 1;

Result:

title              | length | rental_rate
--------------------+--------+-------------
Catch Amistad      |    183 |        0.99
Haunting Pianist   |    181 |        0.99
Intrigue Worst     |    181 |        0.99
Love Suicides      |    181 |        0.99
Smoochy Control    |    184 |        0.99
(10 rows)

Chaining multiple AND conditions

You can chain as many conditions as needed. All must evaluate to TRUE for a row to pass the filter:

SELECT title, rating, length, rental_rate
FROM film
WHERE rating = 'PG'
  AND length BETWEEN 90 AND 120
  AND rental_rate <= 2.99;

AND with OR: precedence and parentheses

AND has higher operator precedence than OR, meaning it is evaluated first. This can lead to unexpected results when mixing them without parentheses:

-- Without parentheses: AND binds tighter, so this means:
-- (rating = 'G' AND length > 100) OR rental_rate < 1
WHERE rating = 'G' AND length > 100 OR rental_rate < 1;

-- Use parentheses to make intent explicit:
WHERE (rating = 'G' OR rental_rate < 1) AND length > 100;

Always use parentheses when combining AND and OR to avoid subtle logic errors.

NULL behavior with AND

Because any comparison with NULL produces NULL (not TRUE or FALSE), a condition like column = NULL never returns rows. Use IS NULL or IS NOT NULL explicitly:

-- Correct: find active customers with no phone on file
SELECT customer_id, first_name
FROM customer
WHERE active = 1
  AND phone IS NULL;

Reference: PostgreSQL documentation — Logical Operators.