PostgreSQL LEFT() function

LEFT() function

The PostgreSQL left() function is used to extract n number of characters specified in the argument from the left of a given string. When the value of n is negative, the extraction will happen from left except last n characters.

Uses of LEFT() Function

• Extracting Substrings: Retrieve a specific number of characters from the start of a string.


• Handling Negative Values: Extract characters from the left side while excluding a specified number of characters from the end.


• Filtering Data: Use in WHERE clauses to filter results based on a prefix match.


• Data Formatting: Format and display portions of text data in a structured manner.


• Combining with Other Functions: Use alongside other string functions for complex text manipulations.


• Data Validation: Check for specific patterns or prefixes in text data for validation purposes.

Syntax:

left(string,n) 

PostgreSQL Version: 9.3

Visual Presentation of PostgreSQL LEFT() function

Example: PostgreSQL LEFT() function:

In the example below, the left function extracted 3 characters from the left of the string 'w3resource'.

SQL Code:

SELECT left('w3resource',3)
AS "Extract 3 characters from the left";

Output:

 Extract 3 characters from the left
------------------------------------
 w3r
(1 row)

Example: PostgreSQL LEFT() function using negative value:

In the example below, the left function extracted all the characters from the left side except 3 rightmost characters from the string 'w3resource', because the value of extracting character number is negative.

SQL Code:

SELECT left('w3resource',-3)
AS "Extract all characters except 3 rightmost";

Output:

 Extract all characters except 3 rightmost
-------------------------------------------
 w3resou
(1 row)

Example: PostgreSQL LEFT() function using columns of table:

Sample Table: employees

If we want to display the first_name, last_name for those employees whose first 3 characters of their name contain 'Nan' from employees table, the following sql statement can be used:

SQL Code:

SELECT first_name, last_name 
FROM employees 
WHERE left(first_name,3)='Nan';

Output:

 first_name | last_name
------------+-----------
 Nancy      | Greenberg
 Nanette    | Cambrault
 Nandita    | Sarchand
(3 rows)

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