【2019年8月版本】OCP 071认证考试最新版本的考试原题-第11题

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

(自链接其实跟两张表的链接同样。能够是等链接、左右外链接等等。

不过在进行内链接时为了区别表的名字，须要加别名

select w.ename,m.ename

from emp2 w

inner join emp2 m

on w.mgr=m.empno;

)