current position：Home>In the Oracle subquery, the from is not a table but a condition. Why
In the Oracle subquery, the from is not a table but a condition. Why
2022-02-03 01:37:57 【CSDN Q & A】
select s1.sno, s1.sname
from student s1
where not exists(select *
from (select_ cno_ from course where tno = (select tno from teacher where tname = ' Xiaohong ‘)) c
where not exists(select * from sc s2 where s2.sno = s1.sno and s2.cno = c.cno));
Just started practicing Oracle, Found a set of questions , There is this sentence in it from The sub query followed by is a cno Field , Not a watch It has an alias behind it c, This last c It can only be used c.cno, Cannot use other fields .
Refer to the answer 1：
(select_ cno_ from course where tno = (select tno from teacher where tname = ' Xiaohong ‘)) c
Refer to the answer 2：
Refer to the answer 3：
Because there is only one field in the sub query cno, So you need to call the results in the sub query , There must be only one cno It's ready to use .
If you want to use other fields , Just find it out .
such as ：cno、name etc. .
(select cno,name from course where tno = (select tno from teacher where tname = ' Xiaohong ‘)) c
Refer to the answer 4：
author[CSDN Q & A],Please bring the original link to reprint, thank you.
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