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admin

使用左外部联接联接两个表，并根据右表列填充新的列值

sql

我有两个表exam_table和emp_table，在这里我想使用左外部联接来联接两个表，并且我想使用右表中的exam_completed_date列创建一个名为new_column的新列。

select id, exam_completed_date from exam_table;

id exam_completed_date 
0  12-01-2019
1  12-12-2019

select id, week_end_date from emp_table where id=0;

id week_end_date
0  11-29-2019
0  11-30-2019
0  12-31-2019
0  12-01-2019
0  12-02-2019
0  12-03-2019
0  12-04-2019

select id, week_end_date, exam_completed_date 
from emp_table emp left outer join 
     exam_table exam 
     on (exam.id=emp.id and exam.exam_completed_date=emp.week_end_date)
where id=0

id week_end_date exam_completed_date 
0  11-29-2019    
0  11-30-2019
0  12-31-2019
0  12-01-2019     12-01-2019
0  12-02-2019    
0  12-03-2019    
0  12-04-2019

我需要这样的输出

id week_end_date exam_completed_date  new_column
0  11-29-2019    
0  11-30-2019
0  12-31-2019
0  12-01-2019     12-01-2019           12-01-2019
0  12-02-2019                          12-01-2019
0  12-03-2019                          12-01-2019 
0  12-04-2019                          12-01-2019

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2021-07-01

共1个答案

admin

我认为您需要一个累积的最大窗口函数：

select id, week_end_date, exam_completed_date,
       max(exam_completed_date) over (partition by id order by week_end_date) as newcolumn
from emp_table emp left outer join
     exam_table exam 
     on exam.id=emp.id and
        exam.exam_completed_date = emp.week_end_date
where id = 0;
2021-07-01