PostgreSQL Tutorial: TRIM Function

August 1, 2023

Summary: In this tutorial, you will learn how to use PostgreSQL TRIM() function to remove the longest string that contains spaces or a particular character from a string.

Table of Contents

Introduction to PostgreSQL TRIM function

The TRIM() function removes the longest string that contains a specific character from a string. By default, the TRIM() function remove spaces (‘ ‘) if you don’t specify explicitly which character that you want to remove.

With the TRIM() function, you can remove the longest string containing a character from the start, end, or both the start and end of a string. Note that a string can be any of the following data types: char, varchar, and text.

The TRIM() function is very useful when we want to remove the unwanted characters from a string in the database. We often use it for data cleansing.

The following illustrates the syntax of the TRIM() function.

TRIM([LEADING | TRAILING | BOTH] [characters] FROM string)

For example, if you want to remove spaces from the beginning of a string, you use the following syntax:

TRIM(LEADING FROM string)

The following syntax of the TRIM() function removes all spaces from the end of a string.

TRIM(TRAILING FROM string)

And to remove all spaces at the beginning and ending of a string, you use the following syntax:

TRIM(BOTH FROM string)

Or just simply:

TRIM(string)

PostgreSQL TRIM function examples

See the following examples of removing leading, trailing, and both leading and trailing spaces from strings.

SELECT
	TRIM (
		LEADING
		FROM
			'  PostgreSQL TRIM'
	),
	TRIM (
		TRAILING
		FROM
			'PostgreSQL TRIM   '
	),
	TRIM ('  PostgreSQL TRIM  ');

PostgreSQL TRIM function examples

The following statement updates the first_name and last_name columns of the customer table in the sample database with the values that do not have leading and trailing spaces. It uses the TRIM() function to remove both leading and trailing spaces from the first_name and last_name columns.

UPDATE customer
SET first_name = TRIM (first_name),
    last_name = TRIM (last_name);

The following statement removes leading zero (0) from a number. Because the TRIM() function only accepts a string as the argument, we have to use type cast to convert the number into a string before passing it to the TRIM() function.

SELECT
	TRIM (
		LEADING '0'
		FROM
			CAST (0009100 AS TEXT)
	); -- 9100

PostgreSQL LTRIM, RTRIM, and BTRIM functions

PostgreSQL provides you with LTRIM, RTRIM and BTRIM functions that are the shorter version of the TRIM() function.

The LTRIM() function removes all characters, spaces by default, from the beginning of a string.
The RTRIM() function removes all characters, spaces by default, from the end of a string.
The BTRIM() function is the combination of the LTRIM() and RTRIM() functions.

The syntax of LTRIM() and RTRIM() function are as follows:

LTRIM(string, [character]);
RTRIM(string, [character]);
BTRIM(string, [character]);

This is equivalent to the following syntax of the TRIM() function:

TRIM(LEADING character FROM string); -- LTRIM(string,character)
TRIM(TRAILING character FROM string); -- RTRIM(string,character)
TRIM(BOTH character FROM string); -- BTRIM(string,character)

Let’s take a look at the following examples of using the LTRIM(), RTRIM() and BTRIM() functions to remove the character e from the enterprise string:

SELECT
	LTRIM('enterprise', 'e');

PostgreSQL LTRIM example

SELECT
	RTRIM('enterprise', 'e');

PostgreSQL RTRIM example

SELECT
	BTRIM('enterprise', 'e');

PostgreSQL BTRIM example

Removing whitespace characters from a string

Sometimes, your string may contain whitespace characters such as space, tab, line break, etc., that you want to remove. However, the TRIM() function only allows you to remove leading and trailing spaces, not all other whitespace characters. You can call the TRIM() function multiple times but it is not efficient.

One way to remove the leading and trailing whitespace characters from a string is to use REGEXP_REPLACE() function. For example, the following statement removes a space and a tab character from the end of the enterprise string with 1 space and 1 tab characters at the end of the string.

SELECT REGEXP_REPLACE('enterprise 	', '\s+$', '');

The \s+$ pattern is explained as follows:

\s : regular expression class shorthand for whitespace.
+ means 1 or more consecutive matches.
$ means the end of the string.

You use the ^\s+ regular expression if you want to remove leading whitespace characters.

In this tutorial, we have shown you how to use the TRIM(), LTRIM(), RTRIM(), and BTRIM functions to remove characters from the beginning, ending, and both in a string.