SQL Server User-Defined Functions - A Beginner's Guide


SQL Server user-defined functions (UDFs) are powerful tools for encapsulating custom logic that can be reused in queries and applications. In this beginner's guide, we'll explore the basics of UDFs, their types, usage, and provide sample code snippets to help you get started with creating and using functions in SQL Server.


Why Use User-Defined Functions?

UDFs offer several advantages:


  • Code Reusability: You can encapsulate commonly used logic and reuse it in multiple queries and applications.
  • Abstraction: UDFs abstract complex logic, making queries more readable and maintainable.
  • Performance: Well-designed UDFs can improve query performance by optimizing and centralizing logic.

Types of User-Defined Functions

SQL Server supports different types of UDFs:


  • Scalar Functions: Return a single value, such as a string or number.
  • Table-Valued Functions: Return a result set that can be used in queries.
  • Inline Table-Valued Functions: Return a table variable and can be used in the FROM clause of a query.

Creating a Scalar Function

Let's create a simple scalar function that calculates the square of a number:


-- Create a scalar function
CREATE FUNCTION dbo.Square (@Number FLOAT)
RETURNS FLOAT
AS
BEGIN
    RETURN @Number * @Number;
END;

Using a Scalar Function

Now, let's use the "Square" function in a query:


-- Use the Square function
SELECT EmployeeName, dbo.Square(Salary) AS SalarySquare
FROM Employees;

What's Next?

As you become more proficient with SQL Server UDFs, explore advanced topics like creating table-valued functions, understanding performance considerations, and using UDFs in stored procedures and views.