基于大多数行的分配顺序在mysql数据库中不为空

Posted 2023-03-31

【中文标题】基于大多数行的分配顺序在mysql数据库中不为空

【英文标题】：Assign order based on most rows are not null in mysql database

【发布时间】：2020-07-20 10:14:21

【问题描述】：

我正在为变量生成所有组合并插入到临时表中

select *
from (select 33 as age union all select null) a cross join
     (select 44 as totaldd union all select null) t cross join
     (select 30 as timeperiod union all select null) d cross join
     (select CURDATE() as StartDateTime union all select null) s

结果是：

我希望基于大多数行的顺序不为空 Like

【参考方案1】：

如果您运行的是 mysql 8.0，您可以使用 dense_rank() 和条件表达式来执行此操作：

select 
    a.age, 
    t.totaldd, 
    d.timeperiod, 
    s.startdatetime,
    dense_rank() over(order by 
          (a.age is null) 
        + (t.totaldd is null) 
        + (d.timeperiod is null) 
        + (s.startdatetime is null)
    ) as rn
from (select 33 as age union all select null) a cross join
     (select 44 as totaldd union all select null) t cross join
     (select 30 as timeperiod union all select null) d cross join
     (select CURDATE() as startdatetime union all select null) s

实际上你甚至可以不使用窗口函数，只使用条件表达式：

select 
    a.age, 
    t.totaldd, 
    d.timeperiod, 
    s.startdatetime,
    1 + (a.age is null) 
        + (t.totaldd is null) 
        + (d.timeperiod is null) 
        + (s.startdatetime is null) as rn
from (select 33 as age union all select null) a cross join
     (select 44 as totaldd union all select null) t cross join
     (select 30 as timeperiod union all select null) d cross join
     (select CURDATE() as startdatetime union all select null) s