如何正确编写这个“简单”的T-SQL查询

Question

我参加了一系列T-SQL练习测试。除了其中一个，我做得很好。我拍了一张照片，以便稍后找出正确的答案。我不认为自己是专家，但我知道我的方式围绕SQL。然而，我不能写出一个不那么难以提出的问题。

以下是练习：

我可能需要按名称分组并总结价格，但我仍然有点迷失。帮助这一个！谢谢

Answer 1

我会这样做：

SELECT 
  people.name, 
  sum(case when sales.fk_people is not null then 1 else 0) as total_sales,
  sum(coalesce(sales.price,0.0)) as total_amount
FROM people  
LEFT JOIN sales ON people.id = sales.fk_people
GROUP BY people.id
-- Could also be ORDER BY sum(coalesce(sales.price,0.0)) desc
ORDER BY people.id;

Answer 2

这是一个非常简单的GROUP BY，带有COUNT（）和SUM（）。这两个表也需要加入：

SELECT name, count(*) as total_sales, sum(price) as total_amount
FROM people INNER JOIN sales ON people.id = sales.fk_people
GROUP BY name;

Answer 3

你也可以试试这个

SELECT 
p.Name
,ISNULL(s.Total_Sales,0) AS Total_Sales
,ISNULL(s.Total_Amount,0) AS Total_Amount
FROM people p  
LEFT JOIN 
(
    SELECT 
    fk_people
    ,COUNT(*) AS Total_Sales
    ,SUM(Price) AS Total_Amount  
    FROM Sales
    GROUP BY fk_people
) s ON p.ID = s.fk_people