您可以使用窗口功能来实现这一点。您应该始终按非聚合字段进行分组。

select
    Type,
    CountPerType,
    100.0 * CountPerType/sum(CountPerType) over () as columnName
from
(
    SELECT 
        Type, 
        count(*) as CountPerType
    FROM myTable
    WHERE Date between 20200101 and 20200131
    GROUP BY 
        Type
) subq

我将编写没有子查询的查询。可以混合使用窗口函数和聚合函数：

SELECT Type,  COUNT(*) as CountPerType,
       COUNT(*) * 100.0 / SUM(COUNT(*)) OVER () as percentage
FROM t
WHERE Date BETWEEN 20200101 AND 20200131
GROUP BY Type;

我不知道性能是否与使用子查询的版本不同（这至少应该是一样好的）。但问题显然更简单。