在另一个答案中建议的case条件在这里是多余的，因为count总是只计算非空记录。因此，您可以简化查询：

SELECT
      id 
    , COUNT(log) AS attended 
    , COUNT(*) - COUNT(log) AS missed
    , IF(COUNT(*) > 0, count(log) / COUNT(*), NULL) AS percentage
FROM
    logs
GROUP BY
    id 
ORDER BY
    attended

此外，我还根据op固定了百分比计算。

“条件聚合”解决了这个问题，基本上你把一个 case expression 内部 count() 功能

SELECT
      id 
    , count(case when log IS NOT NULL then 1 end) AS attended 
    , count(case when log IS NULL then 1 end)     AS Missed
    , case when count(case when log IS NOT NULL then 1 end) > 0 then
           count(case when log IS NOT NULL then 1 end) / count(*)
           else 0
      end AS perc  
GROUP BY id 
ORDER BY attended

如果你使用 count(*) 比所有行都要计数，但是如果计算的值可以为null，则不计算这些null。