Exercises - Part 1

Exercise 1

Create a view that meets the following three conditions (the view name is ViewPractice5_1). Using the product table as the reference table, it is assumed that the table contains 8 rows of data in the initial state.

• Condition 1: the sales unit price is greater than or equal to 1000 yen.
• Condition 2: the registration date is September 20, 2009.
• Condition 3: it includes three columns: commodity name, sales unit price and registration date.

The result of executing the SELECT statement on the view is as follows.

SELECT * FROM ViewPractice5_1;

results of enforcement

product_name | sale_price | regist_date
--------------+------------+------------
T shirt         | 　 1000    | 2009-09-20
 kitchen knife          |    3000    | 2009-09-20

Exercise Code:

CREATE VIEW ViewPractices5_1(product_name, sale_price, regist_date)
AS
SELECT product_name, sale_price, regist_date 
FROM product
WHERE sale_price >= 1000
AND regist_date = '2009-09-20';

Exercise 2

Add viewpractice5 to the view created in exercise 1_ What results will be obtained by inserting the following data into 1?

INSERT INTO ViewPractice5_1 VALUES (' knife ', 300, '2009-11-02');

Exercise results:

An error will be reported when inserting data.

Error Code: 1423. Field of view 'shop.viewpractices5_1' underlying table doesn't have a default value

Exercise 3

Write a SELECT statement based on the following results, where sale_price_all is the average selling unit price of all goods.

product_id | product_name | product_type | sale_price | sale_price_all
------------+-------------+--------------+------------+---------------------
0001       | T shirt         | clothes         | 1000       | 2097.5000000000000000
0002       | Punch        | Office Supplies      | 500        | 2097.5000000000000000
0003       | motion T Shirt       | clothes          | 4000      | 2097.5000000000000000
0004       | kitchen knife          | kitchenware      | 3000       | 2097.5000000000000000
0005       | pressure cooker        | kitchenware      | 6800       | 2097.5000000000000000
0006       | Fork          | kitchenware      | 500        | 2097.5000000000000000
0007       | Dish cleaning board        | kitchenware       | 880       | 2097.5000000000000000
0008       | ball pen        | Office Supplies       | 100       | 2097.5000000000000000

Exercise Code:

SELECT product_id,
product_name,
product_type,
sale_price,
(SELECT AVG(sale_price) 
FROM product) AS sale_price_all
FROM product;

Exercise 4

Please write an SQL statement according to the conditions in exercise 1 and create a view (named AvgPriceByType) containing the following data.

product_id | product_name | product_type | sale_price | avg_sale_price
------------+-------------+--------------+------------+---------------------
0001       | T shirt         | clothes         | 1000       |2500.0000000000000000
0002       | Punch         | Office Supplies     | 500        | 300.0000000000000000
0003       | motion T Shirt        | clothes        | 4000        |2500.0000000000000000
0004       | kitchen knife          | kitchenware      | 3000        |2795.0000000000000000
0005       | pressure cooker         | kitchenware     | 6800        |2795.0000000000000000
0006       | Fork          | kitchenware      | 500         |2795.0000000000000000
0007       | Dish cleaning board         | kitchenware     | 880         |2795.0000000000000000
0008       | ball pen         | Office Supplies     | 100         | 300.0000000000000000

Exercise Code:

CREATE VIEW AvgPriceByType
AS 
SELECT product_id,
product_name,
product_type,
sale_price,
(SELECT AVG(sale_price)
FROM product p2
WHERE p2.product_type = p1.product_type
GROUP BY product_type) AS avg_sale_price
FROM product p1;

Exercises - Part 2

Exercise 5

When an operation or function contains NULL, the result will all become NULL? (judgment question)

Exercise results:

Yes, all become NULL.

Exercise 6

What results can be obtained by executing the following two SELECT statements on the product table used in this chapter?

① The result is returned to the punch, 320 yuan; Wipe the kitchen board, 790 yuan

SELECT product_name, purchase_price
  FROM product
 WHERE purchase_price NOT IN (500, 2800, 5000);

② The result is empty

SELECT product_name, purchase_price
  FROM product
 WHERE purchase_price NOT IN (500, 2800, 5000, NULL);

Exercise 7

Classify the items in the product table in exercise 6.1 as follows according to the sales_price.

• Low grade goods: the sales unit price is less than 1000 yen (T-shirts, office supplies, forks, kitchen cleaning boards, ball point pens)
• Middle grade goods: the sales unit price is more than 1001 yen and less than 3000 yen (kitchen knife)
• High end goods: the sales unit price is more than 3001 yen (Sports T-shirt, pressure cooker)

Please write a SELECT statement to count the quantity of goods contained in the above commodity categories. The results are as follows.

results of enforcement

low_price | mid_price | high_price
----------+-----------+------------
        5 |         1 |         2

Exercise Code:

SELECT 
COUNT(CASE WHEN sale_price <= 1000 THEN product_name ELSE NULL END) AS low_price,
COUNT(CASE WHEN sale_price > 1000 AND sale_price <= 3000 THEN product_name ELSE NULL END) AS mid_price,
COUNT(CASE WHEN sale_price > 3000 THEN product_name ELSE NULL END) AS high_price
FROM product;