Stored Procedures vs. Functions in MS SQL Server: Differences & Use Cases

When working with Microsoft SQL Server, both Stored Procedures and Functions are powerful tools for encapsulating logic and reusing SQL code. However, they serve different purposes and come with their own sets of rules, limitations, and best-use scenarios. In this blog, we’ll break down the key differences between stored procedures and functions, and help you understand when to use which.

What is a Stored Procedure?

A Stored Procedure is a compiled set of SQL statements that can perform operations such as data manipulation (INSERT, UPDATE, DELETE), control flow, and calling other procedures.

Key Characteristics:

  • Can return zero, one, or many results.

  • Can have input/output parameters.

  • Allows use of control-of-flow constructs (IF, WHILE, etc.).

  • Can perform changes to the database (e.g., modify data).

  • Supports TRY...CATCH blocks for error handling.

  • Cannot be used in a SELECT statement.

What is a Function?

A Function (specifically, a user-defined function or UDF) is a SQL object that returns a single value or a table. Functions are meant to be deterministic and side-effect free.

Key Characteristics:

  • Always returns a value (scalar or table).

  • Cannot make permanent changes to database data.

  • Cannot use TRY...CATCH for error handling.

  • Cannot call stored procedures.

  • Can be used inside SELECT, WHERE, and other SQL statements.

Key Differences

Feature Stored Procedure Function
Return Type 0 or more result sets Single value or table
DML Operations Allowed (INSERT, UPDATE, DELETE) Not allowed (read-only)
Usage in SELECT Statement Not allowed Allowed
Error Handling Supports TRY...CATCH Not supported
Input/Output Parameters Input and Output supported Only Input supported
Transaction Control Yes No
Calling from another SQL Executed with EXEC Called within a query

Use Cases

Use a Stored Procedure when:

  • You need to perform multiple DML operations.

  • You need error handling via TRY...CATCH.

  • You need complex business logic and control flow.

  • You’re working with large operations or batch processes.

Use a Function when:

  • You need to return a calculated value in a SELECT clause.

  • You need reusable logic that doesn’t modify data.

  • You want to filter rows using logic in a WHERE clause.

  • You want something easily testable and modular.

Final Thoughts

Understanding the distinctions between stored procedures and functions in SQL Server can help you write more maintainable and efficient SQL code. Use each tool where it fits best: stored procedures for tasks and actions, and functions for computations and expressions.

Use the right tool for the job, and your database will thank you for it!

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