多表查询练习

-- 部门表
CREATE TABLE dept (
  id INT PRIMARY KEY PRIMARY KEY, -- 部门id
  dname VARCHAR(50), -- 部门名称
  loc VARCHAR(50) -- 部门所在地
);

-- 添加4个部门
INSERT INTO dept(id,dname,loc) VALUES 
(10,'教研部','北京'),
(20,'学工部','上海'),
(30,'销售部','广州'),
(40,'财务部','深圳');



-- 职务表，职务名称，职务描述
CREATE TABLE job (
  id INT PRIMARY KEY,
  jname VARCHAR(20),
  description VARCHAR(50)
);

-- 添加4个职务
INSERT INTO job (id, jname, description) VALUES
(1, '董事长', '管理整个公司，接单'),
(2, '经理', '管理部门员工'),
(3, '销售员', '向客人推销产品'),
(4, '文员', '使用办公软件');



-- 员工表
CREATE TABLE emp (
  id INT PRIMARY KEY, -- 员工id
  ename VARCHAR(50), -- 员工姓名
  job_id INT, -- 职务id
  mgr INT , -- 上级领导
  joindate DATE, -- 入职日期
  salary DECIMAL(7,2), -- 工资
  bonus DECIMAL(7,2), -- 奖金
  dept_id INT, -- 所在部门编号
  CONSTRAINT emp_jobid_ref_job_id_fk FOREIGN KEY (job_id) REFERENCES job (id),
  CONSTRAINT emp_deptid_ref_dept_id_fk FOREIGN KEY (dept_id) REFERENCES dept (id)
);

-- 添加员工
INSERT INTO emp(id,ename,job_id,mgr,joindate,salary,bonus,dept_id) VALUES 
(1001,'孙悟空',4,1004,'2000-12-17','8000.00',NULL,20),
(1002,'卢俊义',3,1006,'2001-02-20','16000.00','3000.00',30),
(1003,'林冲',3,1006,'2001-02-22','12500.00','5000.00',30),
(1004,'唐僧',2,1009,'2001-04-02','29750.00',NULL,20),
(1005,'李逵',4,1006,'2001-09-28','12500.00','14000.00',30),
(1006,'宋江',2,1009,'2001-05-01','28500.00',NULL,30),
(1007,'刘备',2,1009,'2001-09-01','24500.00',NULL,10),
(1008,'猪八戒',4,1004,'2007-04-19','30000.00',NULL,20),
(1009,'罗贯中',1,NULL,'2001-11-17','50000.00',NULL,10),
(1010,'吴用',3,1006,'2001-09-08','15000.00','0.00',30),
(1011,'沙僧',4,1004,'2007-05-23','11000.00',NULL,20),
(1012,'李逵',4,1006,'2001-12-03','9500.00',NULL,30),
(1013,'小白龙',4,1004,'2001-12-03','30000.00',NULL,20),
(1014,'关羽',4,1007,'2002-01-23','13000.00',NULL,10);



-- 工资等级表
CREATE TABLE salarygrade (
  grade INT PRIMARY KEY,   -- 级别
  losalary INT,  -- 最低工资
  hisalary INT -- 最高工资
);

-- 添加5个工资等级
INSERT INTO salarygrade(grade,losalary,hisalary) VALUES 
(1,7000,12000),
(2,12010,14000),
(3,14010,20000),
(4,20010,30000),
(5,30010,99990);

-- 查询所有员工信息。查询员工编号，员工姓名，工资，职务名称，职务描述
/*
	1.表单
		员工编号，员工姓名，工资 emp;职务名称，职务描述 job
	2.内联结
		条件
			emp.job_id=job.id;
*/
Select t1.id,t1.salary,t1.ename,t2.jname,t2.description
from emp t1,job t2
where t1.job_id=t2.id;

-- 两个内联结
SELECT t1.id,t1.ename,t1.salary,t2.jname,t2.description,t3.loc,t3.dname
from emp t1,job t2,dept t3
WHERE t1.job_id=t2.id AND t1.dept_id=t3.id;

-- 查询员工姓名，工资，工资等级
/*
	1.表单 员工姓名，工资 emp;工资等级 salarygrade;
	2.条件：
		emp.salary between t1.lossalary and t1.hisalary
*/
SELECT t2.ename,t2.salary,t1.*
FROM salarygrade t1,emp t2
WHERE t2.salary BETWEEN t1.losalary AND t1.hisalary;

-- 查询员工姓名，工资，职务名称，职务描述，部门名称，部门位置，工资等级
SELECT t1.ename,t1.salary,t2.dname,t2.loc,t3.jname,t3.description,t4.grade
FROM emp t1,dept t2,job t3,salarygrade t4
WHERE t1.job_id=t3.id
			AND t1.dept_id=t2.id
			AND t1.salary BETWEEN t4.losalary AND t4.hisalary;
			
-- 查询出部门编号，部门名称，部门位置，部门人数
-- 使用子查询
/*
	使用子查询作为虚拟表
	1.部门编号，部门名称，部门位置 dept表 部门人数 emp表
	2.使用分组查询。按照emp.dept_id完成分组，查询count(id)
	3.使用子查询将第二步骤查询结果与dept表进行关联
*/
SELECT dept_id,count(id)
FROM emp
GROUP BY dept_id;

SELECT t1.*,t2.num
FROM dept t1,
		(SELECT dept_id,count(id) num
		FROM emp
		GROUP BY dept_id) t2
where t1.id=t2.dept_id;

-- 查询所有员工姓名及其直接上级的名称，没有领导的员工也需要查询
/*
	1.姓名 emp,直接上级姓名 emp
			emp表的id与mgr是自关联的
	2.条件
			emp.id=emp.mgr;
	3.查询左表数据和交集
	左外联查询
*/

SELECT t1.id,
				t1.ename,
				t1.mgr,
				t2.id,
				t2.ename
FROM emp t1
LEFT JOIN emp t2
ON t1.mgr=t2.id;