1.自然连接实验

create table test_sp(sno int,pno int);
insert into test_sp(sno,pno) values(1,1);
insert into test_sp(sno,pno) values(1,2);
insert into test_sp(sno,pno) values(2,1);
select * from test_sp

create table test_pj(pno int,jno int);
insert into test_pj(pno,jno) values(1,2);
insert into test_pj(pno,jno) values(2,1);
insert into test_pj(pno,jno) values(1,1);
select * from test_pj

create table test_js(jno int,sno int);
insert into test_js(jno,sno) values(2,1)
insert into test_js(jno,sno) values(1,1)
insert into test_js(jno,sno) values(2,2)
select * from test_js

select sno,pno,jno from test_sp natural join test_pj natural join test_js

 2.分析

select sno,pno,jno from test_sp natural join test_pj
select jno,sno,pno from test_sp natural join test_pj
select jno,sno,pno from test_sp natural join test_pj natural join test_js