[英]Joining two tables using left outer join and population a new column values based on the right table column
我有两个表 exam_table 和 emp_table,在这里我想使用左外连接连接两个表,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
我想你想要一个累积最大窗口函数:
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;
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