Chapter 3 complex query

Q1

CREATE VIEW ViewPractice5_1(product_type, sale_price, regist_date)
AS
SELECT product_type, sale_price,regist_date
  FROM product  
 WHERE regist_date = "2009-09-20" and  sale_price>=1000;

Q2

SQL  error  [1423] [HY000]: Field of view 'shop.viewpractice5_1' underlying table doesn't have a default value

Or because of the definition of the view , The view is just a window of the original table , Therefore, it can only modify the content that can be seen through the window .

Q3

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

Q4

SELECT product_id, product_name, product_type, sale_price,
 (SELECT AVG(sale_price)
    FROM product AS p2
  WHERE p1.product_type=p2.product_type
  GROUP BY product_type) AS sale_price_all
FROM product AS P1

Q5

An operation or function contains NULL when , It all turns out to be NULL .

Q6

Running results 1： return purchase_price The result is not 500,2800,5000, And not for NULL The line of .
Running results 2： Return to empty . The operation or function mentioned above contains NULL when , It all turns out to be NULL . Screening contains / Not included NULL The item , use IS NULL or IS NOT NULL.

Q7

SELECT
SUM(CASE WHEN sale_price BETWEEN 0 AND 1000 THEN 1 ELSE 0 END) AS low_price,
SUM(CASE WHEN sale_price BETWEEN 1001  AND 3000 THEN 1 ELSE 0 END) AS mid_price,
SUM(CASE WHEN sale_price>3000 THEN 1 ELSE 0 END) AS high_price
  FROM product;