Understanding Stored Procedures vs Functions in SQL

Stored procedures and functions are types of routines in databases. They have different purposes and features. Here’s a simple comparison.

Stored Procedure

Definition:

A stored procedure is a set of SQL statements that can be run together. It manages database tasks and returns results.

Characteristics:

• Execution: Stored procedures do not return a value directly but can return result sets, multiple values, or status indicators.
• Purpose: Typically used for performing actions such as data manipulation (INSERT, UPDATE, DELETE), complex calculations, or administrative tasks.
• Parameters: Can accept input parameters and provide output parameters. They may also have parameters that are both input and output.
• Call Method: Executed using the CALL or EXEC command in SQL.
• Transaction Control: Can manage transactions (BEGIN, COMMIT, ROLLBACK) within the procedure.
• Error Handling: Often includes error handling mechanisms to manage exceptions.

Example:

-- Creating a stored procedure
CREATE PROCEDURE GetEmployeeDetails(IN employee_id INT)
BEGIN
    SELECT * FROM Employees WHERE id = employee_id;
END;

-- Calling the stored procedure
CALL GetEmployeeDetails(1001);

Use Cases:

• Complex business logic that involves multiple steps.
• Administrative tasks such as data cleanup or batch processing.
• Encapsulating database operations to improve security and maintainability.

Stored Function

Definition:

A stored function is a precompiled routine that performs a specific task and returns a single value. It performs calculations or returns particular values based on input parameters.

Characteristics:

• Execution: Stored functions return a single value, which can be used in SQL expressions or queries.
• Purpose: Typically used for calculating or returning specific values based on input parameters.
• Parameters: Can accept input parameters and return a single output value. They cannot have output parameters.
• Call Method: Invoked in SQL statements as part of expressions or queries, often using the SELECT statement.
• Transaction Control: Cannot manage transactions within the function.
• Error Handling: Limited error handling capabilities compared to procedures.

Example:

-- Creating a stored function
CREATE FUNCTION CalculateSalaryBonus(salary DECIMAL(10, 2)) 
RETURNS DECIMAL(10, 2)
BEGIN
    RETURN salary * 0.10;
END;

-- Using the stored function in a query
SELECT name, CalculateSalaryBonus(salary) AS bonus 
FROM Employees;

Use Cases:

• Performing calculations that need to be integrated into SQL queries.
• Reusing logic across different SQL queries or expressions.
• Returning values that are used within SELECT statements or other SQL constructs.

Key Differences

Feature	Stored Procedure	Stored Function
Return Type	Can return result sets or status indicators.	Returns a single value.
Call Method	Executed using CALL or EXEC commands.	Invoked within SQL statements or expressions.
Parameters	Can have input, output, and input-output parameters.	Can only have input parameters.
Transaction Control	Can manage transactions.	Cannot manage transactions.
Usage Context	Used for performing operations and data manipulation.	Used for calculations and returning values.
Error Handling	Typically includes error handling.	Limited error handling capabilities.

Conclusion

• Stored Procedures are ideal for complex operations. They are helpful for administrative tasks. Use them in scenarios where you must execute a sequence of SQL statements. They offer more control over transactions and error handling.
• Stored Functions are best suited for performing calculations and returning values that can be used in queries and expressions. They are designed to return a single value and are often used within SQL statements to simplify complex expressions.

Choosing between stored procedures and stored functions depends on your specific needs. It also depends on the nature of the operations you need to do.