MySQL練習：職工表和部門表

--職工表
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
) ;

--部門表
CREATE TABLE dept(
    deptno        INT,
    dname        VARCHAR(14),
    loc        VARCHAR(13)
);

--插入數據到職工表
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);

--插入數據到部門表
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');



--練習開始！！！


-- Q1:查詢出高於10號部門的平均工資的員工信息
select *
from emp
where sal>(select avg(sal)
           from emp
           where deptno=10);
           
-- Q2:查詢出比10號部門任何員工薪資高的員工信息
select *
from emp
where sal>(select max(sal)
           from emp
           where deptno=10);
           
--低效率寫法
select *
from emp
where sal>all(select sal
              from emp
              where deptno=10);
           
-- Q3:和10號部門同名同工作的員工信息
select *
from emp e1
where exists(select *
             from emp e2
             where e2.ename=e1.ename and e2.job=e1.job and e2.deptno=10) and e1.deptno<>10;
                         
--另一種寫法（多列子查詢）
select * 
from emp 
where (ename,job) in (select ename,job 
                      from emp 
                      where deptno=10) and deptno<>10;
                         
-- Q4:獲取員工的名字和部門的名字
select ename,dname
from emp e,dept d
where e.deptno=d.deptno;

-- Q5:查詢emp表中經理信息
select *
from emp
where empno in(select distinct mgr
               from emp);

-- Q6:薪資高於10號部門平均工資的所有員工信息
select *
from emp
where sal>(select avg(sal)
           from emp
           where deptno=10);
           
-- Q7:有哪些部門的平均工資高於30號部門的平均工資
select deptno
from emp
group by deptno
having avg(sal)>(select avg(sal)
                 from emp
                 where deptno=30);

-- Q8:工資>JONES工資的員工信息
select *
from emp
where sal>(select sal
           from emp
           where ename='JONES');
                     
--Q9:查詢與SCOTT同一個部門的員工
select *
from emp
where deptno=(select deptno
              from emp
              where ename='SCOTT');
                        
-- Q10:工資高於30號部門所有人的員工信息
select *
from emp
where sal>(select max(sal)
           from emp
           where deptno=30);
                     
-- Q11:查詢工作和工資與MARTIN完全相同的員工信息
select *
from emp e1
where exists(select *
             from emp e2
             where e1.job=e2.job and e1.sal=e2.sal and e2.ename='MARTIN') and ename<>'MARTIN';
                         
--另一種寫法（多列子查詢）
SELECT * 
FROM emp 
WHERE (job,sal) IN (SELECT job,sal 
                    FROM emp 
                    WHERE ename='MARTIN') and ename<>'MARTIN';
                         
-- Q12:有兩個以上直接下屬的員工信息
select *
from emp e1
where (select count(*)
       from emp e2
       where e2.mgr=e1.empno)>2;
             
--另一種方法
SELECT * FROM emp e1 
WHERE e1.empno IN (SELECT e2.mgr 
                   FROM emp e2 
                   GROUP BY e2.mgr 
                   HAVING COUNT(*)>2);
                        
-- Q13:查詢員工編號為7788的員工名稱,員工工資,部門名稱,部門地址
select ename,sal,dname,loc
from emp inner join dept
on empno=7788 and emp.deptno=dept.deptno;

-- Q14:查詢出高於本部門平均工資的員工信息
select *
from emp e1
where sal>(select avg(sal)
           from emp e2
           where e2.deptno=e1.deptno);
                     
-- Q15:列出達拉斯加工作的人中,比紐約平均工資高的人
select *
from emp inner join dept
on sal>(select avg(sal)
        from emp inner join dept
        on emp.deptno=dept.deptno and loc='NEW YORK') and emp.deptno=dept.deptno and loc='DALLAS';
        
-- Q16:查詢7369員工編號,姓名,經理編號和經理姓名
select e1.empno,e1.ename,e1.mgr 經理編號,e2.ename 經理姓名
from emp e1 inner join emp e2
on e1.mgr=e2.empno and e1.empno=7369;

-- Q17:查詢出各個部門薪水最高的員工所有信息
select *
from emp e1
where sal=(select max(sal)
           from emp e2
           where e2.deptno=e1.deptno);

 善於利用相關子查詢編寫SQL查詢語句，可以較為方便，雖然可能會損失查找效率