Introduction
Structured Query Language (SQL) is a widely used programming language for managing relational databases. One of the key features of SQL is the ability to create and use stored procedures and functions. These powerful tools can simplify database management, improve performance, and enhance security.
In this article, we will explain what stored procedures and functions are, how they work, their types, and their differences.
Stored Procedures
A stored procedure is a pre-written SQL code stored on the database server. It can be called from other SQL code or from an application and can perform a variety of tasks, such as retrieving data, updating data, or executing complex calculations.
Stored procedures are commonly used to simplify database management by allowing commonly performed tasks to be executed with a single command. They can also help to improve performance by reducing the amount of data transferred between the database server and client applications.
Types of Stored Procedures
Simple Stored Procedure
A simple stored procedure is the most common type of stored procedure. It contains a single SQL statement or a sequence of SQL statements that perform a specific task.
CREATE PROCEDURE GetEmployees
AS
BEGIN
SELECT * FROM Employees
END
Input Parameters
Stored procedures can also accept input parameters. This allows the stored procedure to be more flexible and can be used with different parameters.
CREATE PROCEDURE GetEmployeeByID
@EmployeeID int
AS
BEGIN
SELECT * FROM Employees WHERE EmployeeID = @EmployeeID
END
Output Parameters
Stored procedures can also have output parameters. This allows the stored procedure to return data to the calling code or application.
CREATE PROCEDURE GetEmployeeCount
@Count int OUTPUT
AS
BEGIN
SELECT @Count = COUNT(*) FROM Employees
END
Functions
Functions in SQL are similar to stored procedures in that they are pre-written SQL code that can be executed from another SQL code or an application. However, functions differ from stored procedures in a few key ways.
First, functions always return a value, whereas stored procedures may or may not return a value. Second, functions can be used in SQL statements, whereas stored procedures cannot. Finally, functions are typically used to perform a specific calculation or operation, whereas stored procedures are more general-purpose.
Types of Functions
Scalar Functions
A scalar function is a function that returns a single value.
CREATE FUNCTION GetEmployeeCount()
RETURNS int
AS
BEGIN
DECLARE @Count int
SELECT @Count = COUNT(*) FROM Employees
RETURN @Count
END
Table Valued Functions
Table-valued functions are functions that return a table as the result set.
CREATE FUNCTION GetEmployeesByDepartment
(@DepartmentID int)
RETURNS TABLE
AS
RETURN
(
SELECT * FROM Employees WHERE DepartmentID = @DepartmentID
)
Differences between Stored Procedures and Functions
The key differences between stored procedures and functions are,
Return value
Functions always return a value, whereas stored procedures may or may not return a value.
Usage
Functions can be used in SQL statements, whereas stored procedures cannot.
Purpose
Functions are typically used to perform a specific calculation or operation, whereas stored procedures are more general-purpose.
Input
Stored procedures can have input/output parameters, while functions only have input parameters.
Conclusion
Stored procedures and functions are powerful tools in SQL that can simplify database management, improve performance, and enhance security. While they have some similarities, they also have important differences in usage and purpose. Understanding these differences is important when deciding which tool to use for a particular task.