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.
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 a longest string containing a character from the start, end, or both 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 string in the database. We often use it for data cleansing.
The following illustrates the syntax of the TRIM function.
1 | 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:
1 | TRIM(LEADING FROM string) |
The following syntax of the TRIM function removes all spaces from the end of a string.
1 | TRIM(TRAILING FROM string) |
And to remove all spaces at both beginning and ending of a string, you use the following syntax:
1 | TRIM(BOTH FROM string) |
Or just simply:
1 | TRIM(string) |
PostgreSQL TRIM function examples
See the following examples of removing leading, trailing, and both leading and trailing spaces from strings.
1 2 3 4 5 6 7 8 9 10 11 12 | SELECT TRIM ( LEADING FROM ' PostgreSQL TRIM' ), TRIM ( TRAILING FROM 'PostgreSQL TRIM ' ), TRIM (' PostgreSQL TRIM '); |
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.
1 2 3 | 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.
1 2 3 4 5 6 | 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
LTRIMfunction removes all characters, spaces by default, from the beginning of a string. - The
RTRIMfunction removes all characters, spaces by default, from the end of a string. - The
BTRIMfunction is the combination ofLTRIMandRTRIMfunctions.
The syntax of LTRIM and RTRIM function are as follows:
1 2 3 | LTRIM(string, [character]); RTRIM(string, [character]); BTRIM(string, [character]); |
This is equivalent to the following syntax of the TRIM function:
1 2 3 | 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 LTRIM, RTRIM , and BTRIM functions to remove the character e from the enterprise string:
1 2 | SELECT LTRIM('enterprise', 'e'); |
1 2 | SELECT RTRIM('enterprise', 'e'); |
1 2 | SELECT BTRIM('enterprise', 'e'); |
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 remove 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.
1 | SELECT REGEXP_REPLACE('enterprise ', '\s+$', ''); |
The \s+$ is explained as follows:
\s: regular expression class shorthand for whitespace.+means 1 or more consecutive matches.$meas end of 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 TRIM, LTRIM, RTRIM, and BTRIM functions to remove characters from the beginning, ending, and both beginning and ending of a string.