MySQL 无法使用 group by 子句处理连接查询

Question

Select deaths.County_Name as County, 
       max(cases.Cumulative_cases) as Cases, 
       max(deaths.Total_Deaths) as Deaths,
           max(deaths.Population2019) as Population2019
From pennsylvaniadeathsbycounty deaths
Join pennsylvaniacasesbycounty cases
    on deaths.County_Name = cases.Jurisdiction
group by County;

我收到以下错误：错误代码：2013。查询期间与 MySQL 服务器失去连接

两个表的 Jurisddiction 和 County_Name 列是相同的。 我想要一张表格，显示每个县的死亡病例以及每个县的人口。 当我运行查询时，它只加载了一段时间，然后返回上述错误。

Answer 1

查询很可能超时，您可以尝试 union all 而不是像这样加入

select County,
       SUM(Cases) Cases,
       SUM(Deaths) Deaths,
       SUM(Population2019) Population2019
from(
Select deaths.County_Name as County, 
       0 as Cases, 
       deaths.Total_Deaths as Deaths,
       deaths.Population2019 as Population2019
From pennsylvaniadeathsbycounty deaths
union all
Select cases.Jurisdiction as County, 
       cases.Cumulative_cases as Cases, 
       0 as Deaths,
       0 as Population2019
From pennsylvaniacasesbycounty cases) a
group by County