Question

几小时前我在sql上问了一个问题，我做了一些改动。

代码看起来不像正确的代码，因为我处于学习阶段，基本上需要在unix上输入每行的这个psql程序....

所以，以下是我的代码

CREATE TABLE customer
(       custID INT PRIMARY KEY,
        customer_name VARCHAR(50),
        customer_address VARCHAR(200)
);

 CREATE TABLE product
(       prodID INT PRIMARY KEY,
        productName VARCHAR(40),
        productPrice NUMERIC(12, 2),
        productManufacturer VARCHAR(50)
);

CREATE TABLE sale
(       saleID INT PRIMARY KEY,
        custID INT
        prodID INT
        saleQuantity INT,
        saleCost NUMERIC(5, 2),
        FOREIGN KEY (prodID) REFERENCES product,
        FOREIGN KEY(custID) REFERENCES customer
);

CREATE TABLE rating
(       prodID,
        custID,
        rating_date DATE PRIMARY KEY,
        rating_stars tinyint,
        FOREIGN KEY (prodID) REFERENCES product,
        FOREIGN KEY (custID) REFERENCES customer
);


SELECT productName
FROM product
WHERE productName = 'FFPXC Corp'
ORDER BY productPrice ASC;

SELECT DISTINCT productName
FROM product, rating
WHERE  product.prodID = rating.prodID AND ratingStars >= 3;

SELECT productName, SUM(saleQuantity) AS revenue
FROM product, sale
WHERE product.prodID = sale.prodID
GROUP BY productName;

SELECT product_name, round(avg(rating_stars), 1) AS avg_stars, MAX(rating_date) AS recent_date
WHERE product.prod_id = rating.prod_id
FROM product, rating
GROUP BY product_name
ORDER BY avg_stars DESC;

现在，我还有一个问题要做，即查看客户是否对1个产品给出了超过1的评级，如果是这种情况，请获得客户给出的最低评级，并将其返回名称为产品和客户的名字。

问题是......我不知道该怎么做.. 我是sql的新手，我仍然试图了解我的第一个编程语言：java并且结果是sql与它非常不同..

我不能使用if语句，所以作为最后的手段，我决定在这里提出问题。

由于

Answer 1

您可以按多个列进行分组，也可以将group by用于具有连接的语句。

 Select min(rating_stars), customer_name, ProductName
 From rating r
    Inner join customer c
       On c.custid = r.custid
    Inner join product p
       On p.prodid=r.prodid
Group by customer_name, ProductName

Ps，我建议你看一下SqlFiddle.com来设置这样的问题的结构和数据。

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