一、练习题
3.1
CREATE VIEW ViewPractice5_1 (product_name, sale_price, regist_date)
SELECT product_name, sale_price, regist_date
FROM product AS product
WHERE sale_price >= 1000
AND regist_date = '2009-09-20';
SELECT * FROM ViewPractice5_1;
3.2
INSERT INTO ViewPractice5_1 VALUES (’ 刀子 ', 300, ‘2009-11-02’);
的结果是：product中添加数据成功，ViewPractice5_1视图中没有数据添加，因为不满足条件
3.3
SELECT product_id, product_name, product_type, sale_price,
(SELECT AVG(sale_price)
FROM product) AS sale_price_avg
FROM product AS p;
3.4
– 创建视图的语句
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：选出了购买价格不是500， 2800和5000的商品
2：NOT IN 中不能包含null，通常返回空；
3.7
SELECT SUM(CASE WHEN sale_price <= 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 >= 3001 THEN 1 ELSE 0 END) AS high_price
FROM product;
