User-Defined FunctionsEarlier in this tutorial we examined several different types of function, including aggregations, ranking functions, casting and conversion, mathematical functions, string processors and date and time functions. These functions accept zero or more parameters and return a single value. Sometimes you will find that the built-in functions do not meet your requirements. In these cases, you can create your own user-defined functions. User-defined functions are similar to those provided by SQL Server as standard. They are given a name and, optionally, a set of parameters. User-defined functions are created for a database and can be used in scripts, stored procedures, triggers and other user-defined functions that are defined within the database. As with stored procedures, they help to modularise your Transact-SQL (T-SQL) code and improve maintainability by allowing you to centralise logic. For example, you could create a function that returns a standard tax rate. If the tax rules change, the function can be modified and all T-SQL that utilises the function would use the new tax rate automatically. User-defined functions can be separated into two main categories. These are scalar functions and table-valued functions.Scalar FunctionsScalar functions are similar to the functions we have used in earlier articles. They can optionally accept one or more parameters and return a single value. The return value is a standard data type but cannot be a Text, NText, Image or Timestamp. Read more: BlackWasp