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Overview

The LENGTH() function is used to find the length of a string, i.e., the number of characters in a given string. It accepts a string as a parameter. Syntax of the length function is illustrated below: 
LENGTH(string)
The input type is a string, and the return type is int, as it returns the number of characters. Special cases:
  • If a null value is passed in the function, i.e., LENGTH(NULL), it will return NULL.
  • If the parameter is an empty string LENGTH("), it will return 0.
  • If the parameter is a space character LENGTH(''), not empty or null, it will return 1 as it is not empty anymore.

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Examples

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#Case 1: Basic LENGTH() function

The below example uses the LENGTH() function to find out the length of a string text: 
SELECT LENGTH ('Oxla PostgreSQL Tutorial');
The final output will be as follows: 
+------------+
| length     |
+------------+
| 24         |
+------------+

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#Case 2: LENGTH() function using columns

Let’s see how the LENGTH() function works on the personal_details table containing the employee’s id, first_name, last_name, and gender of a retail store as columns. 
CREATE TABLE personal_details (
  id int,
  first_name text,
  last_name text,
  gender text
);
INSERT INTO personal_details 
    (id, first_name, last_name, gender) 
VALUES 
    (1,'Mark','Wheeler','M'),
    (2,'Tom','Hanks','M'),
    (3,'Jane','Hopper','F'),
    (4,'Emily','Byers','F'),
    (5,'Lucas','Sinclair','M');

SELECT * FROM personal_details;
The above query will show the following table: 
+-----+-------------+-------------+----------+
| id  | first_name  | last_name   | gender   |
+-----+-------------+-------------+----------+
| 1   | Mark        | Wheeler     | M        |
| 2   | Tom         | Hanks       | M        |
| 3   | Jane        | Hopper      | F        |
| 4   | Emily       | Byers       | F        |
| 5   | Lucas       | Sinclair    | M        |
+-----+-------------+-------------+----------+
The following query returns the last name and the length of the last name from the personal_details table, where the length of the last_name is greater than 5. 
SELECT last_name,length(last_name)
AS "Length of Last Name"
FROM personal_details
WHERE LENGTH(last_name) > 5;
The output displays all those items in the last_name column with a length of more than 5 characters. 
+---------------+-----------------------+
| last_name     | Length of Last Name   |
+---------------+-----------------------+
| Wheeler       | 7                     |
| Hopper        | 6                     |
| Sinclair      | 8                     |
+---------------+-----------------------+