Usage of DATALENGTH in SQL

Returns the number of bytes occupied by any expression.
Syntax
DATALENGTH (expression)
Parameters
Expression
Any type of expression.
Return type
Int
Note
DATALENGTH is particularly useful for varchar, varbinary, text, image, nvarchar, and ntext data types because these data types can be stored
Variable length data.
The result of null datalength is NULL.
The compatibility level may affect the return value. For more information about the compatibility level, see sp_dbcmptlevel.
Example
This example shows the length of the pub_name column in the publishers table.
USE pubs
GO
SELECT length = DATALENGTH (pub_name), pub_name
FROM publishers
Order by pub_name
GO
The following is the result set:
Length pub_name
---------------------------------------------------
20 Algodata Infosystems
16 Binnet & Hardley
21 Five Lakes Publishing
5 GGG & G
18 Lucerne Publishing
14 New Moon Books
17 Ramona Publishers
14 Scootney Books
(8 row (s) affected)