Understanding Table Valued Functions in SQL Server

Welcome, Dev! If you work with SQL Server, you’ve probably heard of user-defined functions (UDFs). These are database objects that allow you to encapsulate code and reuse it throughout your database. In this article, we’ll be focusing on a specific type of UDF – the table valued function.

What are Table Valued Functions?

A table valued function (TVF) is a type of user-defined function that returns a table as its result set. As the name suggests, the result set of a TVF can be treated as a table and used in other parts of your database. TVFs can take parameters, just like regular functions, and can be used in SELECT, JOIN, WHERE, and other SQL statements.

How are TVFs Different from Scalar Functions?

Scalar functions, like their name suggests, return a single value. This value can be of any data type supported by SQL Server, such as integer, string, or date. In contrast, TVFs return a table, which means they can return multiple values of different data types.

Another key difference between scalar functions and TVFs is that scalar functions are usually used within a SQL statement, while TVFs are used as a standalone object. You can use TVFs in SELECT statements, but you can also use them in JOINs, WHERE clauses, and other parts of your database.

Types of Table Valued Functions

There are two types of TVFs in SQL Server:

Inline Table-Valued Functions

An inline TVF returns a table directly in the SELECT statement. It is defined using the RETURNS TABLE syntax, and can take parameters just like any other function. Here’s an example:

Function Name	Description
GetEmployeesByDepartment	Returns a list of employees for a given department

In this example, we’re creating a function called GetEmployeesByDepartment. This function takes a department ID as its parameter and returns a table with two columns – EmployeeID and EmployeeName. We can use this function in a SELECT statement like this:

SELECT * FROM GetEmployeesByDepartment(1)

This will return all employees in the department with ID 1.

Multi-Statement Table-Valued Functions

A multi-statement TVF is defined using the RETURNS TABLE syntax, just like an inline TVF. However, it uses a BEGIN…END block to define its logic. Here’s an example:

Function Name	Description
GetSalesByYear	Returns a list of sales for a given year

In this example, we’re creating a function called GetSalesByYear. This function takes a year as its parameter and returns a table with three columns – ProductName, SalesAmount, and SalesTotal. We can use this function in a SELECT statement like this:

SELECT * FROM GetSalesByYear(2019)

This will return all sales for the year 2019.

Benefits of Table Valued Functions

There are several benefits to using TVFs in your database:

Code Reusability

Since TVFs are functions, you can encapsulate complex logic and reuse it throughout your database. This can help reduce code duplication and make your code more maintainable.

Performance

TVFs can be more efficient than other methods of achieving the same result. For example, if you need to perform a complex calculation on a large dataset, using a TVF can be much faster than performing the same calculation in a SELECT statement.

Flexibility

TVFs can be used in a variety of ways, such as in SELECT statements, JOINs, and WHERE clauses. This flexibility makes them a powerful tool for working with data.

FAQs

What’s the maximum number of rows that a TVF can return?

The maximum number of rows a TVF can return is 2,147,483,647.

Can TVFs be used in stored procedures?

Yes, you can use TVFs in stored procedures just like any other function.

Can TVFs be indexed?

Yes, TVFs can be indexed using non-clustered indexes. This can help improve performance when querying large datasets.

Can TVFs be nested?

Yes, you can nest TVFs within other TVFs.

Can TVFs be used in views?

Yes, you can use TVFs in views just like any other function.

Conclusion

Table valued functions are a powerful tool for working with data in SQL Server. They allow you to encapsulate complex logic, reuse code, and improve performance. By understanding the types of TVFs available and their benefits, you can make better use of them in your database.