Choose two.
Which two statements are true about a self join?
A) The join key column must have an index.
B) It can be a left outer join.
C) It must be a full outer join.
D) It can be an inner join.
E) It must be an equie join.
Answer：BD
(自连接其实跟两张表的连接一样。可以是等连接、左右外连接等等。
不过在进行内连接时为了区别表的名字，需要加别名
select w.ename,m.ename
from emp2 w
inner join emp2 m
on w.mgr=m.empno;
)