Retrieve the maximum length of a VARCHAR column in SQL Server

I want to find the longest VARCHAR in a specific column of a SQL Server table.

Here's an example:

ID = INT IDENTITY
DESC = VARCHAR(5000)

ID | Desc
---|-----
1  | a
2  | aaa
3  | aa

What's the SQL to return 3? Since the longest value is 3 characters?

Use the built-in functions for length and max on the description column:

SELECT MAX(LEN(DESC)) FROM table_name;

Note that if your table is very large, there can be performance issues.

For MySQL, it's LENGTH, not LEN:

SELECT MAX(LENGTH(Desc)) FROM table_name

Watch out!! If there's spaces they will not be considered by the LEN method in T-SQL. Don't let this trick you and use

select max(datalength(Desc)) from table_name