The SQL LEN function is a built-in function that is used to return the length of a given string or expression in characters. The LEN function is commonly used in SQL queries to perform various operations on character data. For example, it can be used to validate the length of input data to ensure that it meets certain requirements. It can also be used to calculate the length of fields in tables, which can be useful when designing database schemas.


The syntax of the LEN function is as follows:


Where string_expression is the string or expression whose length is to be determined.


Here is an example of how the LEN function can be used in a SQL query:

SELECT LEN('Hello, world!') AS StringLength;

This query would return the value 13, which is the length of the string “Hello, world!”.

In addition to the LEN function, many SQL databases also provide other string functions that can be used to manipulate character data, such as SUBSTRING, CONCAT, and REPLACE. These functions can be combined with the LEN function to perform more complex operations on string data.