Oracle SQL-从另一个表中查找2列

Question

我有2张桌子

Reg_table

student_ID   Course_ID   **Register**_status
    1           co_01       enrolled
    2           co_03       pending
    3           co_05       cancelled
    4           co_06       enrolled

Compl_table

student_ID   Course_ID   **Completion**_status
    1           co_01       Attended
    1           co_03       
    3           co_05       
    4           co_06       Attended
    4           co_05       
    6           co_05      

我想基于两个表的'Student_ID'和'Course_ID'的组合，从'Compl_table'中查找一个新状态，作为'Final_status'添加到Reg_table中。 例如，*如果一名学生在co_01上“注册”，然后在co_01上“参加”，则最终状态应为“参加”； *如果“ completion_status”为空白或“ Compl_table”中不存在“ Student_ID”和“ Course_ID”的组合，则最终状态应与“ Register_status”相同，即“已注册”，“待处理”或“已取消” ”。

因此，结果表应如下所示：

student_ID Course_ID **Final**_status
1 co_01 Attended 2 co_03 pending 3 co_05 cancelled 4 co_06 Attended

这可能吗？ 提前致谢。

添加了代码（抱歉，该示例比示例复杂得多）

with reg_table as 

(select 
b.schd_id
,b.DMN_ID
,b.ACT_CPNT_ID
,b.CPNT_TYP_ID
,b.SCHD_DESC
,b.FACILITY_ID
,a.STUD_ID
,a.ENRL_STAT_ID
,a.ENRL_DTE
,c.CMPL_STAT_ID 
from 
 PA_ENROLL_SEAT a
,PA_SCHED b
,pa_cpnt_evthst c 
where
    a.schd_id = b.schd_id
    and
    b.ACT_CPNT_ID = c.CPNT_ID(+)
    and
    a.STUD_ID = c.STUD_ID(+) 
)
update reg_table r
    set CMPL_STAT_ID = (select CMPL_STAT_ID from pa_cpnt_evthst c where 
         c.stud_id = a.stud_id and c.CPNT_ID = b.ACT_CPNT_ID)

where exists (select 1
                  from pa_cpnt_evthst c
                  where c.stud_id = a.stud_id and
                        c.CPNT_ID = b.ACT_CPNT_ID and
                        c.CMPL_STAT_ID is not null
                 )

Answer 1

在Oracle中，您可以执行以下操作：

update reg_table r
    set register_status = (select c.completion_status
                           from compl_table c
                           where c.student_id = r.student_id and
                                 c.course_id = r.course_id
                          )
    where exists (select 1
                  from compl_table c
                  where c.student_id = r.student_id and
                        c.course_id = r.course_id and
                        c.completion_status is not null
                 );

Answer 2

检查是否可行：

Select r.student_ID, r.Course_ID, nvl(c.Completion_status, r.Register_status) as Final_status
From Reg_table R
  left outer join Compl_table C on c.student_ID = r.student_ID and c.Course_ID = r.Course_ID