IT360 Lab 9: Views, Stored Procedures, Triggers

 

DUE: April 9, 2010, BEFORE start of lab

 

This lab should get you familiarized with creating and using views, triggers, and stored procedures. We will use MySQL for this lab. Use your notes, the slides, and online documentation to solve the exercises in the lab.

 

Set-Up

 

·        For this lab you will be using your MySQL database on schooner.cs.usna.edu. Your user account and the database name are mxxxxxx, where xxxxxx is your alpha. You can connect to schooner.cs.usna.edu server by using the user name and password. If you do not remember your password, contact your instructor.

 

·        Using MySQL interactively:

·        Establish a connection to the MySQL server: From “Start”àAll ProgramsàMySQLàMySQL Query Browser. Fill out the information requested:

o       Server Host: schooner.cs.usna.edu

o       Username: mxxxxxx

o       Password:  yourpassword

o       Default Schema: mxxxxxx (xxxxxx is you alpha).

Click “OK”.

·        Write and execute SQL queries: Write the SQL query in the SQL Query Area Response Set tab. Click “Execute” button, or select QueryàExecute from the menu, to execute the current query (the one with the cursor on it). Note that you need to terminate each SQL statement with a semi-colon (;), if you have more that one SQL statement in the window. If you want to execute multiple SQL statement, you can open a script tab, and write your queries there. When you execute the script, all statements in the script execute.

·        Write and execute stored procedures and triggers: You need to open a script tab and  write your code there, then execute the script. Do not forget the DELIMITER statements to change/ restore the default delimiter (;).

 

Preliminaries

 

a)Copy all your files from Lab8 directory to Lab9 directory on your W drive.

 

b)      Connect to the schooner.cs.usna.edu MySQL server by using MySQL Query Browser.

 

c)If the Product table in your database does not have a “QuantityInStock” column, modify the table to add the column:

ALTER TABLE Product add QuantityInStock integer default 0;

 

You should have now some tables similar with these:

 

Product (BarCode, PName, Price, QuantityInStock)

Sale (SaleID, DeliveryAddress, CreditCard)

SaleItem (SaleID, BarCode, Quantity)

 

 

PART 1: Queries and Views

 

Write SQL queries to accomplish the following tasks. Save all answers for this lab in a file called yourlastname_lab9.sql. Make sure you save the file on your X drive and not on the local machine. Write a comment “/* Exercise xx */”, where xx is the exercise number, before each answer. If the answer is not an SQL statement, place the answer between /* … */.

 

 

  1. List all products, with barcode and name, and the sale id and quantity for the sales containing that product, if any (products that were never sold should still be listed in your result)  Hint: use a left join

 

  1. Write a SQL statement to create a view called AllProductsSales based on the query in Exercise 1.

 

Run the SQL statement.

Check in the database (right-clickàRefresh) that the view was created.  

 

  1. A virtual table or view can be used as if it is a table in the database.  Now write a SQL query against the AllProductsSales view as if it was a table: select everything from the AllProductsSales, ordered by BarCode and SaleID.

 

  1. IMPORTANT: The view does not store any data. The data is stored just in the tables used in the definition of view. When a query that uses AllProductsSales is executed, the system first evaluates the query that defines AllProductsSales, and then performs further evaluation of the query that uses the view.

 

To demonstrate this, do the following:

 

a) Insert a row with value for PName = ‘Bread’ in Product table (use INSERT INTO … VALUES …). (You can change the product name to fit your store)

 

b) Execute the query from exercise 3 again.

 

Did the results changed?  Why?

 

  1. (Updates on views)    

 

Run the following query (or the similar query based on your data):

UPDATE AllProductsSales

SET PName = 'French Bread'

WHERE PName = 'Bread'

 

Does the query succeed? Why?

 

Execute “SELECT * FROM Product” and check whether the name of ‘Bread’ product was changed to ‘French Bread’.

 

One reason to use the views: Hide complexity and simplify queries when frequently using the results of a complex query.

 

Example: In C++, would you rather write the code to compute a square root instead of using sqrt()?  Of course not, and the same idea applies to SQL.  Hide complexity and present a simple “replacement” of the complex query.

 

  1. Create a view called ProductProfit to show the barcode, the name of the product, and total_profit. total_profit represents the total profit for that product, which is based on the fraction of the product price that represents the profit margin (assume a fixed 10%), and the quantity of products sold (found in the SaleItem table).  

Hint1: use GROUP BY

Hint2: you can do calculations in the SELECT statement. For example, the following query will display the barcode and the total inventory value for each product:

SELECT BarCode, Price*QuantityInStock AS TotalValue

FROM Product

 

  1. SQL SELECT statement for MySQL has a “LIMIT n” clause that allows you to limit the number of rows returned in the result of a select query. For example “SELECT * FROM Product LIMIT 5” will display first 5 rows from Products table.

 

Write the SQL query on the ProductProfit view to show the top 5 products based on total profit in order of highest profit to lowest profit.

 

  1. (Extra credit)Write the SQL query to achieve the same result as above, but without using the ProductProfit view (you can still use LIMIT n). This query should look more complicated than the query in the previous exercise.

 

  1. (Extra credit): Write the SQL statement to update the total_profit for ‘Bread’ to be $10,000, using the view. Run the query.

 

Does the query succeed? Why?

 

 

PART 2: STORED PROCEDURES

 

Write SQL code/ queries to accomplish the following tasks. Add all answers to the yourlastname_lab9.sql file. If the answer is not an SQL statement, place the answer between /* … */.

 

  1. Create a stored procedure called spInsertProduct that inserts a new product into the database, under some conditions. The stored procedure has as input parameters the barcode, the product name, price, and quantityInStock. The stored procedure should insert a row in the Product table only if the price is greater than 0 and the quantity is greater or equal to 0.

a)      Write and execute the code to create the stored procedure. (Open a script tab in MySQL Query Browser, write the code to change the delimiter, create the stored procedure,  then change the delimiter back, and execute it) You should see the spInsertProduct stored procedure in your database if you right-click and “refresh”.

b)      Try to insert a product with price < 0 into the database by invoking the stored procedure from the MySQL Query Browser. Was the product inserted? Try now to insert a product with price > 0. Was this product inserted?

c)      Extra credit:

Modify your add_product method in the Product class file that you created in Lab 5 to invoke the spInsertProduct procedure instead of directly submitting an INSERT query to the database. Hint: The query you submit to the database should be something like  “call spInsertProduct(xx,yy,zz)”.

 

Add a quantityInStock input field in your form in product_page.php created in Lab 5 and then modify the product_page.php and product.inc.php to process this field. Now you should be able to just insert a product using the web interface (the “insert” button in the form should invoke the modified add_product method in the Product class)

 

PART 3: TRIGGERS

 

Write SQL code/queries to accomplish the following tasks. Add all answers to the yourlastname_lab9.sql file. If the answer is not an SQL statement, place the answer between /* … */.

 

  1. Create a trigger called updateAvailableQuantity that updates the remaining available quantity in the Product table, for every product sold. The trigger should be executed after each insert operation on the SaleItem table: for the product with the given barcode (the one inserted into SaleItem), update the available quantity in Product table to be the old quantity minus the sold quantity.

a)      Write and execute the code to create the trigger.

b)      Either use your application created in the previous lab to buy some product, or manually insert a row in the SaleItem table for an existing sale. Was the quantity in the Product table updated? Why?

 

 

Turn in (due before start of lab on April 9, 2010):

Electronic:

  1. Upload the file yourlastname_Lab9.sql with all your answers to the Lab 9 assignment on the blackboard.

 

Hard-copies:

  1. The completed assignment coversheet. Your comments will help us improve the course.
  2. A hard copy of the file created for this assignment: yourlastname_Lab9.sql. Do not forget the “/* Exercise xx */” comment before the answer for each exercise.