Question

我的数据库有以下结构：

每个地区（CountryStates）都可以有多个城市（Areas）。每个Area都可以有许多旅游景点或兴趣点（POIs）。我想获得每个地区有多少区域和景点的清单。如果没有，我想显示0.

这是我的疑问：

SELECT Tab1.Reg AS Reg, CountAreas, CountPois
FROM
(SELECT 
        c.Name AS Reg, 
        COUNT(a.Id) AS CountAreas
FROM  
       CountryStates as c LEFT JOIN
       Areas AS a ON a.CountryStates_Id = c.Id
GROUP BY c.Name 
) as Tab1 left join
(SELECT 
        c1.Name AS Reg, 
        COUNT(p.Id) AS CountPois
FROM  
       CountryStates as c1 LEFT JOIN
       Areas AS a ON a.CountryStates_Id = c1.Id LEFT JOIN
       POIs AS p ON a.Id = p.Areas_Id
GROUP BY c1.Name 

) as Tab2 on Tab1.Reg = Tab2.Reg

如何只在一个SELECT中进行此查询？

Answer 1

此查询返回相同的结果：

SELECT c.Name AS Reg, 
        COUNT(DISTINCT(a.Id)) AS CountAreas,
        COUNT(p.Id) AS CountPois
FROM CountryStates as c 
    LEFT JOIN Areas as a ON a.CountryStates_Id = c.Id
    LEFT JOIN POIs AS p ON a.Id = p.Areas_Id
GROUP BY c.Name

区域 - 区域 - 兴趣点查询优化

1 个答案: