Mastering SQL Fundamentals: Choosing the Right Tool - Functions or Stored Procedures?

• Purpose: Functions are reusable blocks of code designed to perform specific calculations and return a single value or a result set.
• Structure: Functions always require a RETURNS clause specifying the data type of the returned value. Additionally, they can take input parameters to receive data from the calling statement.
• Example:

CREATE FUNCTION CalculateDiscount(price DECIMAL(10,2), discountRate INT)
RETURNS DECIMAL(10,2)
AS
BEGIN
  DECLARE discountedPrice DECIMAL(10,2);
  SET discountedPrice = price * (1 - discountRate / 100.0);
  RETURN discountedPrice;
END;

• Use Case: We can use this function in a SELECT statement to calculate the discounted price for a product:

SELECT ProductName, Price, CalculateDiscount(Price, 10) AS DiscountedPrice
FROM Products;

• Purpose: Stored procedures are also reusable blocks of code, but they can perform multiple SQL statements, including data manipulation (INSERT, UPDATE, DELETE) and control flow (IF, WHILE). They may or may not return a value.
• Structure: Stored procedures don't require a RETURNS clause, but they can have input and output parameters to receive and return data, respectively.

CREATE PROCEDURE UpdateCustomerAddress
(
  @CustomerID INT,
  @NewAddress NVARCHAR(MAX)
)
AS
BEGIN
  UPDATE Customers
  SET Address = @NewAddress
  WHERE CustomerID = @CustomerID;
END;

• Use Case: We can call this procedure to update the address of a specific customer:

EXEC UpdateCustomerAddress @CustomerID = 123, @NewAddress = '10 Main Street';

• Choosing the right tool:
  • Use functions for calculations and retrieving specific data.
  • Use stored procedures for complex operations involving multiple statements, data manipulation, and control flow.
• Over-engineering: Avoid creating stored procedures for simple tasks that can be done with a single SQL statement.