自连接（SELF JOIN）

create table employee
(

id int,
name nvarchar(10),
leader_id int

);

insert into employee
values
(1,'董事长',null),
(2,'经理',1),
(3,'员工a',2),
(4,'员工b',2);

select
e.id,
e.name as 员工名,
l.name as 领导名 --领导名字
from employee e
left join employee l
on e.leader_id = l.id