Posted on February 13, 2023 by Kevin Guisarde .

SQL Server offers a powerful feature known as User Defined Functions (UDFs), which enables developers to create custom functions tailored to specific tasks. With UDFs, developers can perform specialized operations on data, such as data validation, calculation, or processing. These functions are designed to encapsulate a set of SQL statements and can be utilized in SELECT, INSERT, UPDATE, and DELETE statements. By using UDFs, developers can simplify complex SQL queries and increase the efficiency of their database operations. With this versatile feature, SQL Server provides developers with a powerful tool to enhance the functionality of their applications and streamline their data management processes.

Agenda

1. Introduction to User-Defined Functions in SQL Server
2. Types of User-Defined Functions in the Hospitality Industry
3. Advanced Practice Questions in Hospitality Industry using SQL Server
4. Most Commonly Asked Interview Question in Hospitality Industry using SQL Server
5. Conclusion

Introduction to User-Defined Functions in SQL Server

SQL Server provides a feature called User Defined Functions (UDFs) which allows developers to create custom functions for specific tasks. These functions can be used to perform specific operations on data, like data validation, data calculation, or data processing. UDFs are used to encapsulate a set of SQL statements and can be used in SELECT, INSERT, UPDATE, and DELETE statements.

Types of User-Defined Functions in the Hospitality Industry

There are three types of User Defined Functions in SQL Server: Scalar Functions, Inline Table-valued Functions, and Multi-statement Table-valued Functions.

Scalar Functions

Scalar functions are used to perform operations on single values and return a single value. For example, in the hospitality industry, a scalar function can be used to calculate the total cost of a hotel room based on the number of days and the room rate. The function can be used in a SELECT statement to retrieve the total cost for each room reservation.

Coding example:

CREATE FUNCTION dbo.CalculateRoomCost (@Days INT, @Rate MONEY) 
RETURNS MONEY 
AS 
BEGIN 
  RETURN (@Days * @Rate) 
END 

SELECT dbo.CalculateRoomCost (3, 200) 

The code above creates a scalar function named “CalculateRoomCost” that takes in two parameters, the number of days and the room rate. The function returns the total cost of the room by multiplying the number of days and the room rate. When the SELECT statement is executed, the function is called with the values 3 and 200 and returns the value 600, which is the total cost of a 3-day stay at a room rate of 200.

Inline Table-valued Functions

Inline Table-valued functions are used to return a single-row result set. For example, in the hospitality industry, an inline table-valued function can be used to retrieve the details of a hotel room based on the room number. The function can be used in a SELECT statement to retrieve the details of multiple rooms.

Coding example:

CREATE FUNCTION dbo.GetRoomDetails (@RoomNumber INT) 
RETURNS TABLE 
AS 
RETURN 
( 
  SELECT RoomNumber, RoomType, RoomRate 
  FROM dbo.Rooms 
  WHERE RoomNumber = @RoomNumber 
) 

SELECT * 
FROM dbo.GetRoomDetails (101) 

The code above creates an inline table-valued function named “GetRoomDetails” that takes in a single parameter, the room number. The function returns the details of a room by querying the “Rooms” table and filtering the results based on the room number. When the SELECT statement is executed, the function is called with the value 101 and returns the details of the room with room number 101.

Multi-statement Table-valued Functions

Multi-statement table-valued functions are used to return multiple rows of results. For example, in the hospitality industry, a multi-statement table-valued function can be used to retrieve the details of all rooms in a hotel. The function can be used in a SELECT statement to retrieve the details of all rooms in the hotel.

Coding example:

CREATE FUNCTION dbo.GetAllRoomDetails () 
RETURNS @Rooms TABLE 
( 
  RoomNumber INT, 
  RoomType VARCHAR(50), 
  RoomRate MONEY 
) 
AS 
BEGIN 
  INSERT INTO @Rooms 
  SELECT RoomNumber, RoomType, RoomRate 
  FROM dbo.Rooms 
  
  RETURN 
END 

SELECT * 
FROM dbo.GetAllRoomDetails () 

The code above creates a multi-statement table-valued function named “GetAllRoomDetails”. The function returns a table with the details of all rooms in the hotel by querying the “Rooms” table and inserting the results into a table variable. When the SELECT statement is executed, the function is called and returns the details of all rooms in the hotel.

Advanced Practice Questions in the Hospitality Industry Using SQL Server

To create the tables and records needed for the following advanced practice questions, run the following script:

CREATE TABLE dbo.Rooms ( 
  RoomNumber INT PRIMARY KEY, 
  RoomType VARCHAR(50), 
  RoomRate MONEY 
) 

INSERT INTO dbo.Rooms (RoomNumber, RoomType, RoomRate) 
VALUES 
  (101, 'Standard', 200), 
  (102, 'Deluxe', 250), 
  (103, 'Suite', 300) 
  
CREATE TABLE dbo.Reservations ( 
  ReservationID INT PRIMARY KEY, 
  RoomNumber INT, 
  StartDate DATE, 
  EndDate DATE, 
  TotalCost MONEY, 
  FOREIGN KEY (RoomNumber) REFERENCES dbo.Rooms (RoomNumber) 
) 

INSERT INTO dbo.Reservations (ReservationID, RoomNumber, StartDate, EndDate, TotalCost) 
VALUES 
  (1, 101, '2022-01-01', '2022-01-03', 600), 
  (2, 102, '2022-02-01', '2022-02-03', 750), 
  (3, 103, '2022-03-01', '2022-03-03', 900) 

1. How can we create and utilize a User Defined Function in SQL Server to retrieve the details of all hotel room reservations for a specific room number, taking into account the room number as a parameter input?

Retrieve the details of all reservations for room number 101.

CREATE FUNCTION dbo.GetReservationDetails (@RoomNumber INT) 
RETURNS TABLE 
AS 
RETURN 
( 
  SELECT * 
  FROM dbo.Reservations 
  WHERE RoomNumber = @RoomNumber 
) 

SELECT * 
FROM dbo.GetReservationDetails (101) 

2. How can we create and utilize a User Defined Function in SQL Server to calculate the total cost of all hotel room reservations for a specific room type, taking into account the room type as a parameter input?

Retrieve the total cost of all reservations for room type ‘Standard’.

CREATE FUNCTION dbo.GetReservationCost (@RoomType VARCHAR(50)) 
RETURNS MONEY 
AS 
BEGIN 
  DECLARE @TotalCost MONEY 
  
  SELECT @TotalCost = SUM(TotalCost) 
  FROM dbo.Reservations 
  WHERE RoomNumber IN (SELECT RoomNumber 
                      FROM dbo.Rooms 
                      WHERE RoomType = @RoomType) 
  RETURN @TotalCost 
END 

SELECT dbo.GetReservationCost ('Standard') 

3. How can we create and utilize a User Defined Function in SQL Server to retrieve the average room rate for all rooms in a hotel without having to manually enter any parameters into the function?

Retrieve the average room rate for all rooms.

CREATE FUNCTION dbo.GetAverageRoomRate () 
RETURNS MONEY 
AS 
BEGIN 
  DECLARE @AverageRate MONEY 
  
  SELECT @AverageRate = AVG(RoomRate) 
  FROM dbo.Rooms 
  
  RETURN @AverageRate 
END 

SELECT dbo.GetAverageRoomRate ()

Most Commonly Asked Interview Question in the Hospitality Industry Using SQL Server

Q: What is a User Defined Function in SQL Server and when would you use it?

A: A User Defined Function in SQL Server is a custom function that is created by the developer to perform specific tasks on data. It can be used to perform operations like data validation, data calculation, or data processing. I would use a UDF in situations where I need to perform a specific operation on data repeatedly and I want to encapsulate the logic in a single function. For example, in the hospitality industry, I could create a UDF to calculate the total cost of a hotel room based on the number of days and the room rate. This UDF can then be used in multiple SELECT statements to retrieve the total cost for each room reservation.

Conclusion

In conclusion, User Defined Functions in SQL Server provide a convenient way for developers to create custom functions for specific tasks. The functions can be used in SELECT, INSERT, UPDATE, and DELETE statements to perform operations on data. There are three types of UDFs in SQL Server: Scalar Functions, Inline Table-valued Functions, and Multi-statement Table-valued Functions. The hospitality industry can benefit from using UDFs for tasks such as data calculation, data validation, and data processing.