数据库技术七②（多表查询的练习）

一、准备表

1.部门表

-- 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');

2.职务表

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');

3.员工表

-- 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,'Simeon',4,1004,'2000-12-17','8000.00',NULL,20),
(1002,'Snow',3,1006,'2001-02-20','16000.00','3000.00',30),
(1003,'Lin',3,1006,'2001-02-22','12500.00','5000.00',30),
(1004,'Tang',2,1009,'2001-04-02','29750.00',NULL,20),
(1005,'CiCi',4,1006,'2001-09-28','12500.00','14000.00',30),
(1006,'Song',2,1009,'2001-05-01','28500.00',NULL,30),
(1007,'Liu',2,1009,'2001-09-01','24500.00',NULL,10),
(1008,'Mike',4,1004,'2007-04-19','30000.00',NULL,20),
(1009,'Luo',1,NULL,'2001-11-17','50000.00',NULL,10),
(1010,'Ceng',3,1006,'2001-09-08','15000.00','0.00',30),
(1011,'Jack',4,1004,'2007-05-23','11000.00',NULL,20),
(1012,'Kui',4,1006,'2001-12-03','9500.00',NULL,30),
(1013,'Dargon',4,1004,'2001-12-03','30000.00',NULL,20),
(1014,'Gege',4,1007,'2002-01-23','13000.00',NULL,10);

4.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);

5.表关系结构图

二、题目

     -- 1.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

     SELECT emp.`id`,emp.`ename`,emp.`salary`,job.`jname`,job.`description`
     FROM emp,job
     WHERE emp.`job_id`=job.id

    -- 2.查询员工编号，员工姓名，工资，职务名称，职务描述，部门名称，部门位置

    SELECT        emp.`id`,emp.`ename`,emp.`salary`,job.`jname`,job.`description`,dept.`dname`,dept.`loc`
    FROM emp,job,dept
    WHERE emp.`job_id`=job.id AND emp.`dept_id`=dept.`id`

    -- 3.查询员工姓名，工资，工资等级

     SELECT emp.`ename`,emp.`salary`,salarygrade.*
      FROM emp,salarygrade
      WHERE emp.`salary` BETWEEN salarygrade.`losalary` AND salarygrade.`hisalary`

   -- 4.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  emp.`id`,emp.`ename`,emp.`salary`,job.`jname`,job.`description`,dept.`dname`,dept.`loc` ,salarygrade.*     
    FROM emp,job,dept,salarygrade
    WHERE  emp.`job_id`=job.id 
    AND emp.`dept_id`=dept.`id` 
    AND emp.`salary` BETWEEN salarygrade.`losalary` AND salarygrade.`hisalary`

   -- 5.查询出部门编号、部门名称、部门位置、部门人数

方法一：
   SELECT dept.`id`,dept.`dname`,dept.`loc`,COUNT(emp.`id`)
   FROM emp,dept
   WHERE emp.`dept_id`=dept.`id`
   GROUP BY dept.`id`
方法二：
   	SELECT 
	    t1.`id`,t1.`dname`,t1.`loc` , t2.total
        FROM 
	    dept t1,
	(SELECT
	    dept_id,COUNT(id) total
         FROM 
	    emp
	 GROUP BY dept_id) t2
	 WHERE t1.`id` = t2.dept_id;

  -- 6.查询所有员工的姓名及其直接上级的姓名,没有领导的员工也需要查询

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