舉例介紹mysql多表查詢方法

本文主要給大家舉例介紹mysql多表查詢方法，文章內(nèi)容都是筆者用心摘選和編輯的，具有一定的針對(duì)性，對(duì)大家的參考意義還是比較大的，下面跟筆者一起了解下mysql多表查詢方法吧。

創(chuàng)建示例數(shù)據(jù)表：

#學(xué)生表
create table stu(sid int primary key,sname varchar(10) not null);
#成績(jī)表
create table score (sid int, score int , cid int);
#科目表
create table subjects (cid int primary key,cname varchar(10));
alter table score add constraint fk_score_sid foreign key(sid) references stu(sid);
alter table score add constraint fk_score_cid foreign key(cid) references subjects(cid);

查詢 學(xué)生成績(jī) 和科目名稱

select * from stu,score where stu.sid = score.sid;

查詢學(xué)生的成績(jī) 要求70以上的

select s.sid, s.sname, c.score from stu s,score c where s.sid = c.sid and c.score>70;

查詢所有學(xué)生的成績(jī)

select * from stu s inner join score c on s.sid = c.sid; 
內(nèi)連接相當(dāng)于把兩張表鏈接成一張表查詢 使用inner join 關(guān)鍵詞 條件 使用on 并且Inner 可以省略 
外鏈接查詢 左外連接查詢 以左邊的表為主 左邊表中的數(shù)據(jù)都會(huì)查詢出來 有可能會(huì)產(chǎn)生無用的數(shù)據(jù) 
select s.sid, s.sname, c.score from score c left join stu s on s.sid = c.sid; 
右外鏈接查詢 
select s.sid, s.sname, c.score from score c right join stu s on s.sid = c.sid; 
自然鏈接 :會(huì)自動(dòng)匹配表中相同的字段 沒有外鍵也能自然查詢 
select * from stu natural join score;

查詢所有學(xué)生的分?jǐn)?shù)和考試科目

select s.sid, s.sname, c.score,u.cname from stu s left join score c on s.sid = c.sid join subjects u on c.cid = u.cid; 
三張表查詢時(shí)2條件 n張表n-1條件

創(chuàng)建示例數(shù)據(jù)表：

#員工表
CREATE TABLE emp(
    empno INT,
    ename VARCHAR(50),
    job VARCHAR(50),
    mgr INT,
    hiredate DATE,
    sal DECIMAL(7,2),
    comm decimal(7,2),
    deptno INT
);
INSERT INTO emp values(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
INSERT INTO emp values(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30);
INSERT INTO emp values(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
INSERT INTO emp values(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
INSERT INTO emp values(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
INSERT INTO emp values(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
INSERT INTO emp values(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
INSERT INTO emp values(7788,'SCOTT','ANALYST',7566,'1987-04-19',3000,NULL,20);
INSERT INTO emp values(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
INSERT INTO emp values(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30);
INSERT INTO emp values(7876,'ADAMS','CLERK',7788,'1987-05-23',1100,NULL,20);
INSERT INTO emp values(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
INSERT INTO emp values(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
INSERT INTO emp values(7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);

--  部門表：dept
CREATE TABLE dept(
    deptno INT,
    dname varchar(14),
    loc varchar(13)
);
INSERT INTO dept values(10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO dept values(20, 'RESEARCH', 'DALLAS');
INSERT INTO dept values(30, 'SALES', 'CHICAGO');
INSERT INTO dept values(40, 'OPERATIONS', 'BOSTON');

查詢與 SCOTT 同一個(gè)部門的員工

select ename from emp where deptno = (select deptno from emp where ename=’SCOTT’);

工資高于30號(hào)部門所有人的員工信息

select * from emp where sal>(select max(sal) from emp where deptno = 30);

查詢工作和工資與MARTIN 完全相同的員工信息

select * from emp where (job,sal) in (select job,sal from emp where ename=’MARTIN’);

有兩個(gè)以上有直接下屬的員工信息

select * from emp where empno in (select mgr from emp group by mgr having count(mgr)>=2);

查詢員工編號(hào)為7788的員工名稱 員工工資 部門名稱 部門地址

select e.ename,e.sal,d.dname,d.loc from emp e ,dept d where e.deptno = d.deptno and empno = 7788;

求7369員工編號(hào)、姓名、經(jīng)理編號(hào)和經(jīng)理姓名

select ename,empno from emp where empno in (7369, (select mgr from emp where empno = 7369)); 
select e1.ename,e1.empno,e2.ename,e2.empno from emp e1,emp e2 where e1.mgr = e2.empno and e1.empno = 7369

求各個(gè)部門薪水最高的員工所有信息

select * from emp where (deptno ,sal) in (select deptno,max(sal) from emp group by deptno); 
查詢過程中出現(xiàn)問題 查詢時(shí)沒有把部門的條件帶進(jìn)去 只是按最高工資處理的 可以把查詢結(jié)果返回的結(jié)果集當(dāng)做一個(gè)新表來使用 
select * from emp e1 ,(select deptno,max(sal) msal from emp group by deptno) e2 where e1.sal = e2.msal and e1.deptno = e2.deptno;

看完以上關(guān)于mysql多表查詢方法，很多讀者朋友肯定多少有一定的了解，如需獲取更多的行業(yè)知識(shí)信息 ，可以持續(xù)關(guān)注我們的行業(yè)資訊欄目的。