阿里SQL学习笔记——Task3

本笔记为阿里云天池龙珠计划SQL训练营的学习内容，链接为：https://tianchi.aliyun.com/specials/promotion/aicampsql；

内容会做在一个思维导图中—MySQL笔记 - GitMind

第三次作业

1.
CREATE VIEW ViewPractice5_1 AS
SELECT product_name, sale_price, regist_date
 FROM product
WHERE sale_price >= 1000
 AND regist_date = '2009-09-20'

2.不满足插入条件，会抱错。原条件

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

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

3.5
正确

3.6
（1）选出了价格不为500, 2800, 5000的，且没有null的商品。
（2）not in参数中不能包含null，会返回空

3.7
SELECT SUM(CASE  sale_price  WHEN   <= 1000 THE 1 ELSE 0 END)
AS  low_price;
SUM (CASE sale_price  WHEN  BETWEEN 1001 AND 3000 THE 1 ELSE 0 END) AS mid_price;
SUM(CASE sale_price WHEN >= 3001 THE 1 ELSE 0 END)
AS high_price;
FROM product;