diagram of SQL performance optimization with Functions and Procedures and difference between stored procedure and function

Difference Between Stored Procedure and Function in SQL

Introduction

Stored procedures and functions are essential tools in SQL for modularizing database operations. While they share similarities, their use cases differ significantly. This guide compares stored procedures vs functions, complete with syntax examples, performance implications, and a decision flowchart to help you choose the right too.

What is a Stored Procedure?

A stored procedure is a prepared SQL code that can be saved and reused multiple times. Instead of writing the same query repeatedly, you can store it as a procedure and call it whenever required.

In SQL, a Stored Procedure is a precompiled collection of one or more SQL statements that can be executed as a single unit. It helps improve code reusability, performance, and security by allowing developers to store commonly used queries and call them when needed. Stored procedures are particularly useful in complex database operations, such as data validation, business logic execution, and transaction management. They can accept input parameters, return output values, and handle exceptions efficiently.

Syntax of a Stored Procedure:

CREATE OR REPLACE PROCEDURE <procedure_name>
    (<parameter IN/OUT <datatype>>)
[ IS | AS ]
    <declaration_part>
BEGIN
    <execution_part>
EXCEPTION
    <exception_handling_part>
END;

Example of a Stored Procedure:

CREATE PROCEDURE SelectAllDeveloper
AS
SELECT * FROM developer
GO;

What is a Function?

A function in SQL is a standalone PL/SQL subprogram that performs a specific task. Similar to stored procedures, functions have unique names by which they can be referred. Functions are often used for calculations, data processing, and returning single values.

In SQL, a function is a reusable subprogram designed to perform a specific task and return a single value. Functions are commonly used for calculations, data processing, and formatting results within SQL queries. Unlike stored procedures, functions can be directly used inside SELECT, WHERE, and HAVING clauses, making them highly useful for data manipulation.
Functions help enhance code reusability, improve query efficiency, and maintain modularity in database operations. They can accept input parameters and must return a single output value, making them ideal for computations and transformations within SQL queries.

Syntax of a Function:

CREATE OR REPLACE FUNCTION <function_name>
    (<parameter IN/OUT <datatype>>)
RETURN <datatype>
[ IS | AS ]
    <declaration_part>
BEGIN
    <execution_part>
EXCEPTION
    <exception_handling_part>
END;

Key Differences Between Stored Procedures and Functions:

Below is point of difference between stored Procedure and Function

1. A procedure  contain both input and output parameters, but a function can contain only
 input parameters .
2. Inside a procedure we can use DML Data Manipulation Language (INSERT/UPDATE/DELETE) statements. But inside a function we can't use DML statements.
3. We can't utilize a Stored Procedure in a Select statement. But we can use a function
in a Select statement.
4. We can use a Try-Catch Block in a Stored Procedure but inside a function we can't
use a Try-Catch block for debuging purpose .
5. We can use transaction management in a procedure code but we can't in a function  code.
6. We can't join a Stored Procedure for any use case but we can join functions.
7. Stored Procedures cannot be used in the SQL statements anywhere in the
WHERE/HAVING/SELECT section. But we can use a function anywhere in our Query.
8. A procedure code can return 0 or n values (max 1024). But a function code can return only 1
value that is mandatory .
9. A procedure can't be called from a function but we can able to  call a function from a
procedure in Query.

FAQs on Stored Procedure vs Function in SQL

1. What is the main difference between a stored procedure and a function?
   A stored procedure is used to execute a series of SQL statements and can return multiple values, whereas a function is used for computations and must return a single value.

2. Can a stored procedure return a value like a function?
   Yes, a stored procedure can return multiple values using OUT parameters, while a function must return a single value.

3. Can I use a function inside a SELECT statement?
   Yes, functions can be used in SELECT, WHERE, and HAVING clauses, but stored procedures cannot.

4. Can a function modify database tables?
   No, functions cannot perform INSERT, UPDATE, or DELETE operations, whereas stored procedures can modify database tables.

5. Which one is better for performance: stored procedure or function?
   Stored procedures generally perform better for batch operations and complex logic, while functions are optimized for query execution and readability.

6. Can a function call a stored procedure?
   No, a function cannot call a stored procedure, but a stored procedure can call a function.

7. Can we use transaction management inside a function?
   No, transaction control (COMMIT, ROLLBACK) is not allowed inside functions, but it can be used in stored procedures.

8. Can stored procedures be used in JOIN operations?
   No, stored procedures cannot be used in JOINs, but functions can be used in JOINs to retrieve computed values.

9. Can I use TRY-CATCH in a function?
   No, error handling using TRY-CATCH is only available in stored procedures, not in functions.

10. Which one should I use: a stored procedure or a function?
    Use a function when you need a single calculated value in a query. Use a stored procedure when performing multiple operations, modifying data, or handling complex business logic.

Conclusion:

In this article ,We can choice between a stored procedure and a function depends on the specific requirements of the task and both are important in SQL.
It's often a good practice to take a backup before performing such operations, especially in a production environment.
We provided SQL  Interview Question for learning.

Stored procedures and functions are both powerful features in SQL that help optimize query execution and improve code reusability. While stored procedures are used for complex operations that may involve multiple queries and updates, functions are mainly used for calculations and returning specific values. Choosing between the two depends on the use case and requirements of your SQL operations.