连接查询的内连接问题

Question

查询有哪些不同的上级领导姓名
'select a.empname,(select empname from emptb b where b.empno=a.mgrno) as boss_name from emptb a;

这个我只会写一半，帮我看看，谢谢大家。

Answer 1

SELECT empname AS boss_name FROM epmtb a WHERE EXISTS( SELECT 1 FROM epmtb b WHERE a.empno = b.mgrno );