我正在尝试从日志表中计算出基本的“出勤”报告。我的logs
表如下所示:
TABLE logs
id | date | log |
------------------------|
123 | 2018-01-01 | 1234 |
123 | 2018-01-02 | | // Missed log
123 | 2018-01-03 | 5678 |
456 | 2018-01-01 | 5678 |
456 | 2018-01-02 | 1234 |
456 | 2018-01-03 | 1234 |
因此,空条目将导致错过日期。
所需的SELECT
结果将是这样:
id | perc |
------------|
123 | 0.666 |
456 | 1 |
我已经尝试了以下方法,但是我不确定从这里去哪里
SELECT id, count(*) AS attended WHERE log IS NOT NULL GROUP BY id ORDER BY attended
屈服:
id | attended |
---------------|
123 | 2 |
456 | 3 |
这使我成为其中的一部分,但是我不确定如何向其中添加missed
列,然后计算百分比。稍后,我将结果添加到“用户”表中,以便将名称与日志id
关联。任何帮助将不胜感激!
答案 0 :(得分:4)
CASE条件在这里仅作为COUNT always counting NOT NULL records是多余的。结果,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,我已经按照OP确定了百分比计算。
答案 1 :(得分:1)
“条件聚合”解决了这个问题,基本上是将case expression
放在count()
函数中
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
如果您使用count(*)
,则所有行都将被计数,但是如果您计算的值可以为NULL,则不会计算这些NULL。