在 Mysql 中使用 First_Value 函数时值错误

Question

我需要根据这个table准备一份报告，我只能阅读：

想法是根据更高的 activity 识别为每个观察结果获取最后一个值。例如，观察 10 的值对应于 activity 数字 19。

到目前为止，这是我的代码：

select 
first_value(text) over (partition by employee order by case when observation = 10 then activity else 0 end desc) as "Obs 10",
first_value(number) over (partition by employee order by case when observation = 20 then activity else 0 end desc) as "Obs 20",
first_value(dropdown) over (partition by employee order by case when observation = 40 then activity else 0 end desc) as "Obs 40"
-- the same for the rest of the observations
from employee_proc

但是，该员工可能与其他在执行查询时尚未注册的观察相关联。

如果我为这个员工包含这段代码：

...
first_value(text) over (partition by employee order by case when observation = 120 then activity else 0 end desc) as "Obs 120",
...

我得到了一个错误的值而不是 null（假设尚未为他注册观察）。

如何避免得到这种结果？。是否有另一种方法来获得最终结果，另一种更优化的方法？

此致。

Answer 1

您在问题中显示的结果可以通过以下查询更有效地实现：

create temporary table max_activity
select observation,max(activity) from employee_proc group by 1;


select employee,
activity,
MAX(IF(observation = 10, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs10,
MAX(IF(observation = 20, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs20,
MAX(IF(observation = 30, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs30,
MAX(IF(observation = 40, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs40,
MAX(IF(observation = 50, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs50,
MAX(IF(observation = 60, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs60,
MAX(IF(observation = 70, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs70,
MAX(IF(observation = 80, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs80,
MAX(IF(observation = 90, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs90,
MAX(IF(observation = 100, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs100,
MAX(IF(observation = 110, ifnull(TEXT_,ifnull(date_in,ifnull(number,dropdown))),NULL)) AS Obs110
from employee_proc
inner join max_activity
on employee_proc.activity = max_activity.activity
group by 1,2;

在 Mysql 中使用 First_Value 函数时值错误

Wrong value when using First_Value function in Mysql

mysql

function

partition