mysql - 行的百分比

Question

让以下查询的结果“总计”:

SELECT COUNT(DISTINCT C1) from T where <something>

(“something”是 T 列上的长条件)。

让“partial1”的结果为:

SELECT COUNT(DISTINCT C1) from T where <something> AND C2>10.

和“partial2”的结果:

SELECT COUNT(DISTINCT C1) from T where <something> AND C3>20.

有更好的方法来编写返回比率“partial1/total”和“partial2/total”的查询吗？如果总计为零，则任何通常的默认值都可能有效(null、-1、1、100...)。

Answer 1

如果您确实需要在 MySql 级别完成此操作，您可以尝试以下操作:

SELECT
    partial1/total,
    partial2/total
FROM (
    SELECT 
        COUNT(DISTINCT C1) as total,
        COUNT(DISTINCT IF(C2>10, C1, NULL)) as partial1,
        COUNT(DISTINCT IF(C3>20, C1, NULL)) as partial2
    FROM T
    WHERE <something>
) as tmp
;