SQL Server: Function or Stored Procedure – Which Should You Choose?

SQL Server Functions and Stored Procedures: Selection Guide

In SQL Server, choosing between a function or a stored procedure depends on the needs of the specific task. The following analysis will help you make informed decisions:

Function

Functions are specialized for calculations that return scalar values, such as calculations, string operations, or conditional evaluations. They cannot make permanent changes to the database (for example, INSERT or UPDATE statements). Functions can be embedded directly into SQL statements or used in joins to retrieve results.

Stored Procedure

A stored procedure, on the other hand, is a PL/SQL block that encapsulates multiple SQL statements. They are mainly used to perform complex database operations such as data retrieval, manipulation or business logic. Stored procedures can have parameters, execute multiple statements, and return output or modify the database.

When to use functions

• When you need the result of a calculation or operation as a scalar value.
• When you want to simplify queries by referencing calculations or operations from reusable components.
• When a calculation or operation does not require database modification.

When to use stored procedures

• When you need to perform multiple operations, control the execution flow, or handle complex business logic.
• When you need to interact with multiple tables, perform updates or inserts, or perform transactions.
• When you want to encapsulate reusable logic and simplify maintenance.

Other notes

As @Sean K Anderson emphasized, functions follow the definition of a computer science function, which is to return a value without changing the parameters. Stored procedures, on the other hand, can modify data, have optional parameters, and don't always return a value.

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