MySQL多表练习案例1

员工_工资等级多表练习

数据准备

    -- 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);

需求

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
    	t1.`id`,-- 员工编号
    	t1.`ename`,-- 员工姓名
    	t1.`salary`, -- 工资
    	t2.`jname`, -- 职务名称
    	t2.`description` -- 职务描述
    FROM
    	emp t1 ,job t2
    WHERE
    	t1.`job_id` = t2.`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
    	t1.`id`,
    	t1.`ename`,
    	t1.`salary`,
    	t2.`jname`,
    	t2.`description`,
    	t3.`dname`,
    	t3.`loc`
    FROM
    	emp t1,
    	job t2,
    	dept t3
    WHERE
    	t1.`job_id` = t2.`id` AND
    	t1.`dept_id` = t3.`id`;

3.查询员工姓名，工资，工资等级

    SELECT
    	t1.`ename`,
    	t1.`salary`,
    	t2.`grade`
    FROM
    	emp t1,
    	salarygrade t2
    WHERE t1.`salary` BETWEEN t2.`losalary` AND t2.`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.`ename`,
    	emp.`salary`,
    	job.`jname`,
    	job.`description`,
    	dept.`dname`,
    	dept.`loc`,
    	salarygrade.`grade`
    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

SELECT 
	dept.*,
	COUNT(emp.`id`)
FROM
	emp RIGHT JOIN
	dept
ON
	emp.`dept_id` = dept.`id`
GROUP BY 
	emp.`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
    	a.`ename`, -- 员工姓名
    	a.`mgr`, -- 员工上级编号
    	b.`id`,-- 员工编号
    	b.`ename` -- 员工上级姓名
    FROM
    	emp a
    	LEFT JOIN 
    	emp b
    ON
    	a.`mgr` = b.`id`;

注：以上代码都是亲手手打，本人初学者，难免有一些低级错误出现，希望大佬们指正！ 分享自己练习的案例，一起进步一起学习！