Sql server® 2012 t-sql fundamentals

User-Defined Functions

The purpose of a user-defined function (UDF) is to encapsulate logic that calculates something, pos-

sibly based on input parameters, and return a result. 

SQL Server supports scalar and table-valued UDFs. Scalar UDFs return a single value; table-valued 

UDFs return a table. One benefit of using UDFs is that you can incorporate them in queries. Scalar 

UDFs can appear anywhere in the query where an expression that returns a single value can appear 

(for example, in the SELECT list). Table UDFs can appear in the FROM clause of a query. The example 

in this section is a scalar UDF.

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