MySQL多表查詢

//方式一

create
table stu(sid int
primary
key,sname varchar(20),age int);
//方式二
create
table stu(sid int,sname varchar(20),age int, primary
key(sid));
//方式三
create
table stu(sid int,sname varchar(20),age int);
alter
table stu add
primary
key(sid);
//刪除主鍵
alter
table stu drop
primary
key;

//1.從表

create table dept(
deptno int primary key,
dname varchar(20)
);insert into dept value(10,"研發部");
insert into dept value(20,"財務部");
insert into dept value(30,"運營部");
//2.主表
create table emp(
empno int primary key,
ename varchar(20),
deptno int,
constraint fk_emp_dept foreign key (deptno) references dept(deptno)
);

//1.從表

create table hasband(
hid int primary key,
hname varchar(20)
);select * from hasband;
insert into hasband value(1,"劉備");
insert into hasband value(2,"關羽");
insert into hasband value(3,"張飛");
//2.主表（主表的主鍵作為外來鍵）
create table wife(
wid int primary key,
wname varchar(20),
constraint fk_wife_hasband foreign key(wid) references hasband(hid)
);insert into wife value(1,"小喬");
insert into wife value(2,"貂蟬");
insert into wife value(3,"吳氏");

//學生表

create table student(
sid int primary key,
sname varchar(20)
);//老師表
create table teacher(
tid int primary key,
tname varchar(20)
);//關聯表
create table stu_tea(
sid int,
tid int,
constraint fk_stu foreign key(sid) references student(sid),
constraint fk_tea foreign key(tid) references teacher(tid)
);insert into student value(1,"老大");
insert into student value(2,"老二");
insert into student value(3,"老三");
insert into student value(4,"老四");
insert into student value(5,"老五");
insert into teacher value(1,"***");
insert into teacher value(2,"張老師");
insert into teacher value(3,"劉老師");
insert into teacher value(4,"武老師");
insert into stu_tea value(1,1);
insert into stu_tea value(2,1);
insert into stu_tea value(3,1);
insert into stu_tea value(4,1);
insert into stu_tea value(5,1);
insert into stu_tea value(1,2);
insert into stu_tea value(2,2);
insert into stu_tea value(3,2);
insert into stu_tea value(2,3);
insert into stu_tea value(3,3);
insert into stu_tea value(4,3);
insert into stu_tea value(5,3);
insert into stu_tea value(3,4);
insert into stu_tea value(4,4);
insert into stu_tea value(5,4);

合併結果集

連線查詢
內連線左外連線
右外連線
子查詢

create table aa(a int,b varchar(20));

create table bb(c int,d varchar(20));
//1.查詢全部
select * from aa
union all
select * from bb;
//2.去重複查詢
select * from aa
union all
select * from bb;

//1.方言

select * 
from emp,dept
where emp.deptno = dept.deptno;
//2.標準
select * 
from emp inner join dept
on emp.deptno = dept.deptno
//3.自然
select * 
from emp natural join dept

select * 

from emp left outer join dept
on emp.deptno = dept.deptno

select * 

from emp right outer join dept
on emp.deptno = dept.deptno

左外連線與右外連線合併結果集去重複就是全外連線

//查詢工資高於諸葛亮的員工資訊

select * 
from emp
where sal >(select sal from emp where ename="諸葛亮");

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