Stored Functions vs. Procedures

Introduction Definitions Key Differences Code Examples Best Practices FAQ

Introduction

In database development, stored functions and procedures play a crucial role in encapsulating business logic and improving performance. Understanding the distinctions between them is vital for effective database design and maintenance.

Definitions

Stored Procedure

A stored procedure is a precompiled collection of one or more SQL statements that can be executed as a single unit. Procedures can accept input parameters and can return multiple values through output parameters.

Stored Function

A stored function is similar to a stored procedure but is designed to return a single value. Functions can be called from SQL statements, enabling them to be utilized in SELECT queries or other expressions.

Key Differences

Return Value: Procedures do not return values directly, while functions always return a single value.
Usage: Procedures are called using the CALL statement, whereas functions are invoked as part of an expression.
Parameter Types: Functions can only use input parameters, while procedures can use input and output parameters.

Code Examples

Stored Procedure Example


CREATE PROCEDURE GetEmployeeCount()
BEGIN
    SELECT COUNT(*) FROM Employees;
END;

Stored Function Example


CREATE FUNCTION GetEmployeeCount() 
RETURNS INT
BEGIN
    DECLARE empCount INT;
    SELECT COUNT(*) INTO empCount FROM Employees;
    RETURN empCount;
END;

Best Practices

Use stored procedures for operations that require multiple SQL statements.
Use stored functions to encapsulate reusable logic that returns a value.
Keep procedures and functions focused on a specific task to maintain clarity and reusability.
Document your code to ensure maintainability and ease of understanding for other developers.

FAQ

Can a stored procedure call a function?

Yes, a stored procedure can call a stored function, allowing you to use the function's return value within the procedure.

Are there performance differences between functions and procedures?

Generally, stored procedures can be more efficient for complex operations since they can execute multiple SQL statements in a single call, while functions are typically used for simpler calculation tasks.

Can functions modify database state?

No, functions should not modify the database state and are intended to return a value. Use procedures for operations that change database data.