看CSDN测试后，关于领导职工显示的问题！！！

create table staff(staff_id int,staff_name varchar(6))---建测试表,职工表


go


insert staff


select 1,'小王' union all


select 2,'小刘' union all


select 3,'赵科长'union all


select 4,'吴经理' union all


select 5, '董主任'


go


select * ---------------显示表记录


from staff


go


create table staff_leader_relation(staff_id int ,leader_id int )----建立员工关系表


alter table staff_leader_relation add constraint pk_relation foreign key(staff_id) references staff(staff_id) -----表外建FK


go


alter table staff add constraint pk primary key nonclustered(staff_id)---------------- PK


alter table staff_leader_relation add constraint pk2_relation foreign key(leader_id) references staff(staff_id)


go


select *


from staff_leader_relation --- 此时为空，可先为两个有外键联系的表先建立外键约束，再输入记录


go


insert staff_leader_relation


select 1,3 union all


select 2,3 union all


select 3,4 union all


select 5,4


go


select *


from staff_leader_relation


----展现出-----------------------------------------------------------------


staff_name leader_name


----------------------------------------------------------------------------------


select x.staff_name,y.staff_name as leader_name ---------我作的，可显示，但是没有作业领导职工的人显示不出来


from staff x,staff_leader_relation s,staff y


where x.staff_id=s.staff_id and s.leader_id=y.staff_id






select distinct a.staff_name,c.staff_name as leader_name from staff a,staff_leader_relation b,staff c -------- 同上


where a.staff_id=b.staff_id


and b.leader_id=c.staff_id


order by a.staff_name






select ---------------splory给出的完整答案，包括职工吴经理(null)


(select staff_name from staff where staff_id=a.staff_id) xiashu


,(select staff_name from staff where staff_id=b.leader_id) lingdao


from staff a left join sl_ralation b


on a.staff_id=b.staff_id








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select A.staff_name,B.staff_name -----------中山大学开出答案


from staff A,staff B,sl_ralation C


where A.staff_id=C.staff_id and B.staff_id=C.leader_id


union


select A.staff_name,null


from staff A


where A.staff_id not in (select staff_id from sl_ralation)