PostgreSQL Tutorial: LIKE

Summary: in this tutorial, you will learn how to use the PostgreSQL LIKE and ILIKE operators to query data using pattern matchings.

Table of Contents

Introduction to PostgreSQL LIKE operator

Suppose that you want to find a customer, but you don’t remember her name exactly. However, you can recall that her name begins with something like Jen.

How do you find the exact customer from the database? You may find the customer in the customer table by looking at the first name column to see if there is any value that begins with Jen. However, this process can be time-consuming if the customer table has a large number of rows.

Fortunately, you can use the PostgreSQL LIKE operator to match the first name of the customer with a string using the following query:

SELECT
	first_name,
    last_name
FROM
	customer
WHERE
	first_name LIKE 'Jen%';

Notice that the WHERE clause contains a special expression: the first_name, the LIKE operator and a string that contains a percent sign (%). The string 'Jen%' is called a pattern.

The query returns rows whose values in the first_name column begin with Jen and may be followed by any sequence of characters. This technique is called pattern matching.

You construct a pattern by combining literal values with wildcard characters and use the LIKE or NOT LIKE operator to find the matches. PostgreSQL provides you with two wildcards:

• Percent sign (%) matches any sequence of zero or more characters.
• Underscore sign (_) matches any single character.

The syntax of PostgreSQL LIKE operator is as follows:

value LIKE pattern

The expression returns true if the value matches the pattern.

To negate the LIKE operator, you use the NOT operator as follows:

value NOT LIKE pattern

The NOT LIKE operator returns true when the value does not match the pattern.

If the pattern does not contain any wildcard character, the LIKE operator behaves like the equal (=) operator.

PostgreSQL LIKE operator – pattern matching examples

Let’s take some examples of using the LIKE operator

Simple PostgreSQL LIKE examples

See the following example:

SELECT
	'foo' LIKE 'foo', -- true
	'foo' LIKE 'f%', -- true
	'foo' LIKE '_o_', -- true
	'bar' LIKE 'b_'; -- false

How it works.

• The first expression returns true because the foo pattern does not contain any wildcard character so the LIKE operator acts like the equal (=) operator.
• The second expression returns true because it matches any string that begins with the letter f and followed by any number of characters.
• The third expression returns true because the pattern (_o_) matches any string that begins with any single character, followed by the letter o and ended with any single character.
• The fourth expression returns false because the pattern b_ matches any string that begins with the letter b and followed by any single character.

It’s possible to use wildcards at the beginning and/or end of the pattern.

For example, the following query returns customers whose first name contains er string like Jenifer, Kimberly, etc.

SELECT
	first_name,
    last_name
FROM
	customer
WHERE
	first_name LIKE '%er%'
ORDER BY 
        first_name;

You can combine the percent (%) with underscore (_) to construct a pattern as the following example:

SELECT
	first_name,
	last_name
FROM
	customer
WHERE
	first_name LIKE '_her%'
ORDER BY 
        first_name;

The pattern _her% matches any string that:

• Begin with any single character (_)
• And is followed by the literal string her.
• And is ended with any number of characters.

The returned first names are Cheryl, Sherri, Sherry, and Therasa.

PostgreSQL NOT LIKE examples

The following query uses the NOT LIKE operator to find customers whose first names do not begin with Jen:

SELECT
	first_name,
	last_name
FROM
	customer
WHERE
	first_name NOT LIKE 'Jen%'
ORDER BY 
        first_name

PostgreSQL extensions of LIKE operator

PostgreSQL supports the ILIKE operator that works like the LIKE operator. In addition, the ILIKE operator matches value case-insensitively. For example:

SELECT
	first_name,
	last_name
FROM
	customer
WHERE
	first_name ILIKE 'BAR%';

The BAR% pattern matches any string that begins with BAR, Bar, BaR, etc. If you use the LIKE operator instead, the query will not return any row.

PostgreSQL also provides some operators that act like the LIKE, NOT LIKE, ILIKE and NOT ILIKE operator as shown below:

In this tutorial, you have learned how to use the PostgreSQL LIKE and ILIKE operators to query data using pattern matching.

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PostgreSQL Tutorial