【2019年8月版本】OCP 071認證考試最新版本的考試原題-第11題

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

(自鏈接其實跟兩張表的鏈接同樣。能夠是等鏈接、左右外鏈接等等。

不過在進行內鏈接時爲了區別表的名字，須要加別名

select w.ename,m.ename

from emp2 w

inner join emp2 m

on w.mgr=m.empno;

)