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
(In fact, since the connection of two tables with the same connection can be connected and so on, and so on around the external connection.
But during the connector to distinguish the name of the table, you need to add an alias
select w.ename,m.ename
from emp2 w
inner join emp2 m
on w.mgr=m.empno;
)