SQL DATALENGTH

The SQL Server DATALENGTH is used to return the number of bytes used to represent a specified expression. The syntax of DATALENGTH is

SELECT DATALENGTH (String_Expression)
FROM [Source]

This DATALENGTH function is useful for VARCHAR, NVARCHAR, VARBINARY, TEXT, NTEXT, and IMAGE Data Types because these data types will store the data length. For this example, We are going to use the below-shown table.

SQL DATALENGTH Example

The DATALENGTH Function is used to return the number of bytes used to represent a given expression. The following query will show multiple ways to use it.

The first four lines of SQL Server code are used to declare the string variable of Data Type Varchar and Nvarchar and assign the same data to both variables.

In the below two statements, We used the SQL DATALENGTH function to find the data length of both variables. We also assigned a new name to that result as ‘Data Length’ using the ALIAS Column.

In the next line, We used it directly on the string.

DECLARE @String_Exp VARCHAR(50)
SET @String_Exp = 'Learn SQL Server' 

DECLARE @Str_Exp NVARCHAR(50)
SET @Str_Exp = 'Learn SQL Server' 
 
SELECT DATALENGTH(@String_Exp) AS 'Data Length' 
SELECT DATALENGTH(@Str_Exp) AS 'Data Length'
 
--Finding directly
SELECT DATALENGTH('SQL Server Tutorial') AS 'Data Length'
SELECT DATALENGTH('SQL Server') AS 'Data Length'

The DATALENGTH function also allows you to find the number of bytes in a column. In this example, We are going to find the Data length of a Department Name and Email columns.

SELECT [FirstName]
      ,[LastName]
      ,[DepartmentName]
      ,DATALENGTH([DepartmentName]) AS [Dept Data Length]
      ,[Email]
      ,DATALENGTH([Email]) AS [Email Data Length]
 FROM [Employe]