Question

我正在尝试解决这个问题。

返回一个表，该表列出了语言和发言者人数，但仅包括具有> 200,000,000发言者的语言？根据发言人数量将这些结果从高到低排序

这是我的代码：

SELECT 
    Language,
    Percentage / 100 AS 'Percentage',
    SUM(Population) AS Population,
    Population * Percentage AS 'Speakers'
FROM 
    language
GROUP BY 
    Language
HAVING 
    Speakers > 200000000;

有人可以帮我吗？

Answer 1

您可以在下面尝试使用演说者的计算表达式进行

SELECT 
     Language,
     Percentage/100 AS 'Percentage',
     SUM(Population) AS Population,
     SUM(Population)*(Percentage/100) AS 'Speakers'
FROM language
GROUP BY Language
HAVING SUM(Population)*(Percentage/100)> 200000000
ORDER BY SUM(Population)*(Percentage/100) DESC

Answer 2

请勿对列别名使用单引号。那真是个坏习惯。仅对字符串和日期常量使用单引号。

SQL（通常）允许您在ORDER BY中引用列别名。有些数据库还允许您在HAVING子句中引用它们-但不是全部。

我不确定Percentage应该做什么。它应该在GROUP BY中。在其他情况下，Percentage应该是聚合计算的一部分：

SELECT Language,
       SUM(Percentage * Population / 100) / SUM(Population) AS Percentage,
       SUM(Population) AS Population,
       SUM(Population * Percentage/100) AS Speakers
FROM language
GROUP BY Language
HAVING SUM(Population*Percentage/100.0) > 200000000
ORDER BY Speakers DESC;

请注意，某些数据库执行整数除法，因此99/100 = 0，而不是0.99。因此，我会这样做：

SELECT Language, 
       SUM(Percentage * Population / 100.0) / SUM(Population) AS Percentage,
       SUM(Population) AS Population,
       SUM(Population*Percentage/100.0) AS Speakers
FROM language
GROUP BY Language
HAVING SUM(Population*Percentage/100.0) > 200000000
ORDER BY Speakers DESC;

具有的SQL问题

2 个答案: