无法按正确顺序打印名称，利润总额也不正确

Question

CREATE TABLE seller_details
(
    seller_id integer PRIMARY KEY, 
    seller_name text
);

CREATE TABLE sales_data
(
    seller_id integer, 
    quantity integer, 
    price_per_item integer
);

INSERT INTO seller_details VALUES (1, 'sam');
INSERT INTO seller_details VALUES (2, 'jack');
INSERT INTO seller_details VALUES (3, 'john');

INSERT INTO sales_data VALUES (1, 4, 100);
INSERT INTO sales_data VALUES (1, 5, 200);
INSERT INTO sales_data VALUES (1, 4, 300);
INSERT INTO sales_data VALUES (2, 2, 500);
INSERT INTO sales_data VALUES (2, 9, 300);
INSERT INTO sales_data VALUES (3, 1, 500);

COMMIT;


SELECT * FROM seller_details;
SELECT * FROM sales_data;

SELECT
    seller_name, 
    (quantity * price_per_item) AS total_sales 
FROM
    seller_details sd, sales_data sda
GROUP BY
    seller_name
ORDER BY
    total_sales DESC

Answer 1

您似乎在聚合中缺少 (quantity*price_per_item) as total_sales 中的 sum，但是您真正的问题是如何在表上进行连接。您的查询正在创建交叉连接（见下文）而不是内部连接，即您正在生成更多记录而不是基于匹配的卖家 ID。我建议以后指定连接类型

下面的查询进行了这些调整

select seller_name, SUM(quantity*price_per_item) as total_sales 
from seller_details sd
inner join sales_data sda ON sd.seller_id = sda.seller_id
group by seller_name
order by total_sales desc

seller_name	total_sales
jack	3700
sam	2600
john	500

View Demo DB Fiddle

我在下面提供了一个交叉连接结果演示，供您仔细阅读。求和后，这些会给您带来比预期更大的 total_sales。

select seller_name, quantity*price_per_item as total_sales 
from seller_details sd,sales_data sda 
order by seller_name

seller_name	total_sales
jack	400
jack	1000
jack	1200
jack	1000
jack	2700
jack	500
john	400
john	1000
john	1200
john	1000
john	2700
john	500
sam	400
sam	1000
sam	1200
sam	1000
sam	2700
sam	500

View on DB Fiddle

让我知道这是否适合你。

无法按正确顺序打印名称，利润总额也不正确

can't print the names in the right order and the sum of profit is wrong as well

sql

database

rdbms