内含 GROUP BY 的 SUM 子查询

Question

我有一个特殊的查询要运行。我需要将每个地区下不同地级市的人口值求和为一列，并将其返回给主查询。例如这个查询：

SELECT region_en 
     , population AS temppop 
  FROM prefectures 
 WHERE region_id = 12 
 GROUP 
    BY region_en

返回此表：

Karditsa 129541
Larissa 279305
Magnesia 206995
Sporades 13798
Trikala 138047

以上所有都属于同一个区域 id (12)，我需要在同一个查询下获得所有这些人口的总和。我尝试应用上述方法，但它不起作用。我没有得到 767686 而是 95960750 的总和：

SELECT SUM(b.cases) as cases
     , COALESCE(SUM(o.poptemp), 0) as pop
  FROM prefectures AS b 
  LEFT 
  JOIN 
     ( SELECT region_en
            , population AS poptemp 
         FROM prefectures 
        WHERE region_id = 12 
        GROUP 
           BY region_en
     ) AS o 
    ON o.region_en = b.region_en
 WHERE b.region_id = '12' 

基本上我需要每个地区的病例总数，以及居住在该地区的所有人的总和。

Answer 1

其实我用了不同的方法。

Select SUM(o.cas) as cases, SUM(o.pop) as population FROM
(SELECT a.population as pop, SUM(a.cases) as cas FROM prefectures a WHERE a.region_id = 12 GROUP BY a.region_en) AS o

这会恢复正确的值，而且速度也非常快。 最后你得到 2 列：

cases population
2515  767686

这是正确的值。

Answer 2

您似乎在寻找窗口总和。您的原始查询不是有效的聚合查询，这使事情有点不清楚。

如果每个region_en只有一行，则不需要聚合：

SELECT region_en, population, SUM(population) OVER() as region_population
FROM prefectures 
WHERE region_id = 12 

您可以像这样一次为所有区域获得相同的结果：

SELECT region_en, population, 
    SUM(population) OVER(PARTITION BY region_id) AS region_population
FROM prefectures 

如果每个region_en 确实有几行：

SELECT region_en, SUM(population) AS population, 
    SUM(SUM(population)) OVER(PARTITION BY region_id) as region_population
FROM prefectures 
GROUP BY region_id, region_en

请注意，窗口函数仅在 MySQL 8.0 中可用。在早期版本中，您可以将查询表述为：

SELECT region_en, population, 
    (SELECT SUM(p1.population) FROM prefectures p1 WHERE p1.region_id = p.region_id) AS region_population
FROM prefectures p