Stored Procedures & Functions in Database

Stored procedures and functions are database objects in SQL that allow you to encapsulate a series of SQL statements into a reusable, named unit. While both can contain SQL code and be executed, they have distinct differences in terms of usage and behavior. Here's a comparison and contrast of stored procedures and functions, along with examples:

Stored Procedures:

1. Purpose:

   • Stored procedures are primarily used for performing a sequence of database operations, including data modification (INSERT, UPDATE, DELETE) and data retrieval (SELECT).
   • They can also be used to encapsulate business logic, such as transaction management, error handling, and complex data manipulations.

2. Return Value:

   • Stored procedures do not return a value directly. They may use output parameters to return values.

3. Example:

   CREATE PROCEDURE sp_GetEmployeeName(@EmployeeID INT) AS BEGIN SELECT FirstName, LastName FROM Employees WHERE EmployeeID = @EmployeeID; END;

   This stored procedure sp_GetEmployeeName takes an EmployeeID as input and returns the employee's first and last names.

4. Usage Scenarios:

   • Use stored procedures when you need to encapsulate a series of SQL statements for data manipulation and perform actions like INSERT, UPDATE, DELETE, and complex queries.
   • Stored procedures are useful for enforcing security and access control, as you can grant execute permissions on procedures without exposing table details.

Functions:

1. Purpose:

   • Functions are primarily used for performing computations on values and returning a single scalar value.
   • They are designed to be used in SQL statements, such as SELECT queries, as part of an expression.

2. Return Value:

   • Functions return a single value or a table variable (in the case of table-valued functions).

3. Example:

   CREATE FUNCTION fn_CalculateTotalPrice(@ProductID INT, @Quantity INT) RETURNS DECIMAL(10, 2) AS BEGIN DECLARE @Price DECIMAL(10, 2); SELECT @Price = UnitPrice FROM Products WHERE ProductID = @ProductID; RETURN @Price * @Quantity; END;

   This scalar-valued function fn_CalculateTotalPrice takes a ProductID and Quantity as inputs and returns the total price.

4. Usage Scenarios:

   • Use functions when you need to perform calculations, transformations, or lookups on data and return a single value as a result.
   • Functions can be used in SELECT statements, WHERE clauses, JOIN conditions, and more.

When to Use One Over the Other:

1. Use Stored Procedures When:

   • You need to perform data manipulation operations (INSERT, UPDATE, DELETE) or complex queries.
   • You want to encapsulate and centralize business logic and error handling.
   • You need to execute a series of SQL statements as a single unit of work.
   • You don't need to return a value directly (though you can use output parameters).

2. Use Functions When:

   • You need to calculate, transform, or look up values and return a single value or a table result.
   • You want to use the function within SQL expressions, such as in SELECT, WHERE, or JOIN clauses.
   • You need to encapsulate reusable computation logic that can be applied in various SQL queries.

In summary, stored procedures are suitable for data manipulation and encapsulating business logic, while functions are best for calculations and transformations that return scalar values. The choice between them depends on your specific requirements and whether you need to return values directly or perform complex operations on data.