string_expression

Is the string expression to be evaluated. string_expression can be a constant, variable, or column of either character or binary data.

bigint if expression is of the varchar(max), nvarchar(max) or varbinary(max) data types; otherwise, int.

The following example selects the number of characters and the data in FirstName for people located in Australia.

USE AdventureWorks;
GO
SELECT LEN(FirstName) AS Length, FirstName, LastName 
FROM Sales.vIndividualCustomer
WHERE CountryRegionName = 'Australia';
GO

Reference

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