Practice Database

• Subqueries
  the CREATE TABLE emp (
  empno INT,
  ename VARCHAR (50),
  the Job VARCHAR (50),
  MGR manager INT,
  the HireDate time employment DATE,
  SAL salary DECIMAL (7,2),
  COMM bonus DECIMAL (7,2),
  deptno department number 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);

CREATE TABLE dept(
deptno INT,
dname VARCHAR(14),
loc 地点 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’);

-- 单行子查询(> < >= <= = <>)
	-- 查询出高于10号部门的平均工资的员工信息

-- 多行子查询(in  not in any all)
	-- 查询出比10号部门任何员工薪资高的员工信息

-- 多列子查询(实际使用较少)
	-- 和10号部门同名同工作的员工信息

-- select 后面接子查询	
	-- 获取员工的名字和部门的名字
	
-- from 后面接子查询
    -- 查询emp表中经理信息
	
-- where 后面接子查询	
	-- 薪资高于10号部门平均工资的所有员工信息
	
-- group by 后面接子查询
	-- 有哪些部门的平均工资高于30号部门的平均工资

	
-- 工资>JONES工资
SELECT ename,sal from emp where emp.sal>(SELECT sal from emp where emp.ename="JONES")
-- 查询与SCOTT同一个部门的员工
SELECT ename from emp where emp.deptno=(SELECT e.deptno from emp e where e.ename="scott" )
-- 工资高于30号部门所有人的员工信息
SELECT * from emp where sal>(SELECT SUM(sal) from emp where deptno=30)
-- 查询工作和工资与MARTIN完全相同的员工信息
SELECT * 
from emp e 
where e.job=(SELECT job from emp where ename="MARTIN") and e.sal=(SELECT sal from emp where ename="MARTIN")
-- 有两个以上直接下属的员工信息
SELECT * 
from emp e 
where e.empno=(SELECT mgr 
from emp  
HAVING (Count(emp.mgr))>3
)
-- 查询员工编号为7788的员工名称,员工工资,部门名称,部门地址
SELECT ename,sal,dname,loc 
from emp , dept 
where dept.deptno=emp.deptno and empno=7788

- SQL查询的综合案例

1. 查询出高于本部门平均工资的员工信息
SELECT DISTINCT e.*
from emp e JOIN emp m
where e.deptno=m.deptno and e.sal>(
SELECT AVG(e.sal) from emp e JOIN emp m where e.deptno=m.deptno)


2. 列出达拉斯加工作的人中,比纽约平均工资高的人
SELECT DISTINCT e.ename
from emp e JOIN dept d
where e.deptno=d.deptno and d.loc="DALLAS" 
and e.sal>(SELECT AVG(e.sal) from emp e where e.deptno=(
SELECT deptno from dept where dept.loc="NEW YORK" ))


3. 查询7369员工编号,姓名,经理编号和经理姓名
SELECT e.empno,e.ename,e.mgr,m.ename 
FROM emp e,emp m 
WHERE e.mgr = m.empno and e.empno=7369;


4. 查询出各个部门薪水最高的员工所有信息
select * 
from emp 
where sal in (
select max(sal) 
from emp 
group by deptno)