SQL查询将列转换为行

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我们可以通过pivot/unpivot函数获取吗？

使用

联合所有人
：

select sum(cases) as [Total cases], sum(deaths) as [Total deaths] 
FROM [myschema].[metrics]

select x.info, sum(x.cnt) cnt
from metrics m
cross join lateral (values ('total cases', m.cases), ('total deaths', m.deaths)) as x(info, cnt)
group by x.info

或者，如果数据库支持横向联接：

select 'total cases' info, sum(cases) cnt from metrics
union all select 'total deaths', sum(deaths) from metrics

最简单的通用方法是
union all
：

select sum(cases) as [Total cases], sum(deaths) as [Total deaths] 
FROM [myschema].[metrics]

select x.info, sum(x.cnt) cnt
from metrics m
cross join lateral (values ('total cases', m.cases), ('total deaths', m.deaths)) as x(info, cnt)
group by x.info

方括号看起来像SQL Server。在这种情况下，我建议采用横向连接：

select 'Total Cases'  as which, sum(cases) 
from [myschema].[metrics]
union all
select 'Total Deaths' as which, sum(deaths)
from [myschema].[metrics];

这只会读取表格一次。如果表确实是一个更复杂的查询（例如视图或CTE），那么性能会有很大的提高。
您也可以使用UNPIVOT来获得所需的结果：

select v.*
from (select sum(cases) as TotalCases, sum(deaths) as TotalDeaths 
      from [myschema].[metrics]
     ) m cross apply
     (values ('TotalCases', TotalCases), ('TotalDeaths', TotalDeaths)
     ) v(which, cnt);

上述数据的输出将为：

   SELECT
    *
FROM
    (
        SELECT
            SUM(cases)      AS total_cases,
            SUM(deaths)     AS total_deaths
        FROM
            myschema.metrics
    ) UNPIVOT ( value
        FOR category
    IN ( total_cases,
         total_deaths ) );
     

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