SQL Server User Defined Functions: Inline Functions Tutorial

What Are Inline User Defined Functions?

Inline user defined functions (inline UDFs) are table-valued functions that return a table result set defined by a single SELECT statement.

Unlike multi-statement functions, inline functions do not have a function body with multiple statements or variable declarations.

They are essentially parameterized views that can be used in queries wherever a table is expected.

• Return a table data type.
• Consist of a single SELECT statement.
• Parameters can be used to filter or customize the returned data.
• Are inlined into the calling query for better performance.

Creating an Inline User Defined Function

To create an inline function, use the CREATE FUNCTION statement with RETURNS TABLE and define the function body as a single RETURN statement containing a SELECT query.

The syntax is straightforward and similar to creating views but with parameters.

• Use CREATE FUNCTION with RETURNS TABLE.
• Define parameters as needed.
• Return a single SELECT statement wrapped in RETURN.

Using Inline Functions in Queries

Once created, inline functions can be used in the FROM clause of a query just like a table or view.

You can join them with other tables or filter their results using WHERE clauses.

• Call the function with parameters in the FROM clause.
• Join with other tables for complex queries.
• Use WHERE, ORDER BY, and other clauses as needed.

Performance Benefits of Inline Functions

Inline functions are optimized by SQL Server's query processor by integrating the function's SELECT statement into the calling query.

This allows the optimizer to generate efficient execution plans, unlike multi-statement functions which can cause performance overhead.

They avoid the context switching and row-by-row processing that can degrade performance.

• Inlined into calling query for optimization.
• Avoids overhead of multi-statement functions.
• Improves query plan efficiency and execution speed.