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，职位名称，职务描述
 CREATE TABLE job(
 id INT PRIMARY KEY,
 jname VARCHAR(20),
 description VARCHAR(50)
 );
 
 -- 添加四个职务
 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, -- 入职时间
   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_dept_id_ref_dept_id_fk FOREIGN KEY (dept_id) REFERENCES dept(id)
   );

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);

-- 练习1
-- 查询所有员工信息。显示员工编号, 员工姓名, 工资, 职务名称, 职务描述
-- 1.根据需求明确查询哪些表 emp job
SELECT * FROM emp INNER JOIN job;
-- 2.明确表连接条件去掉笛卡尔积
SELECT * FROM emp INNER JOIN job ON emp.job_id = job.id;
-- 3.后续的查询

SELECT 
   emp.id AS 员工编号,
   emp.`ename` AS 员工姓名,
   emp.`salary` AS 工资,
   job.`jname` AS 职务名称,
   job.`description` AS 职务描述
FROM
  emp 
  INNER JOIN job 
    ON emp.`job_id` = job.`id` ;

-- 练习2
-- 查询所有员工信息。显示员工编号, 员工姓名, 工资, 职务名称, 职务描述, 部门名称, 部门位置
-- 1.根据需求明确查询哪些表 emp job dept
SELECT * FROM emp INNER JOIN job INNER JOIN dept;

-- 2.明确表连接条件去掉笛卡尔积
SELECT * FROM emp INNER JOIN job ON emp.job_id = job.id INNER JOIN dept ON emp.dept_id = dept.id;
-- 3.后续的查询

SELECT 
  emp.`id` AS 员工编号,
  emp.`ename` AS 员工姓名,
  emp.`salary` AS 工资,
  job.`jname` AS 职务名称,
  job.`description` AS 职务描述,
  dept.`dname` AS 部门名称,
  dept.`loc` AS 部门位置
FROM
  emp 
  INNER JOIN job ON emp.job_id = job.id
  INNER JOIN dept ON emp.`dept_id` = dept.`id`;

-- 练习3
-- 查询经理的信息。显示员工姓名, 工资, 职务名称, 职务描述, 部门名称, 部门位置, 工资等级
-- 1.根据需求明确查询哪些表 emp job dept salarygrade
SELECT * FROM emp INNER JOIN job INNER JOIN dept INNER JOIN salarygrade;
-- 2.明确表连接条件去掉笛卡尔积
SELECT * FROM emp INNER JOIN job ON emp.job_id = job.id INNER JOIN dept ON emp.dept_id = dept.id INNER JOIN salarygrade ON emp.salary BETWEEN salarygrade.losalary AND salarygrade.hisalary;
-- 3.后续的查询

SELECT 
emp.`ename` AS 员工姓名,
emp.`salary` AS 工资,
job.`jname` AS 职务名称,
job.`description` AS 职务描述,
dept.`dname` AS 部门名称,
dept.`loc` AS 部门位置,
salarygrade.`grade` AS 工资等级
FROM emp 
INNER JOIN job ON emp.`job_id` = job.`id`
INNER JOIN dept ON emp.`dept_id` = dept.`id`
INNER JOIN salarygrade ON emp.`salary` BETWEEN salarygrade.`losalary` AND salarygrade.`hisalary`
WHERE job.`jname` = '经理';

-- 练习4
-- 查询出部门编号、部门名称、部门位置、部门人数
-- 1.根据需求明确查询哪些表 dept emp
SELECT * FROM dept INNER JOIN emp;
-- 2.明确表连接条件去掉笛卡尔积
SELECT * FROM dept LEFT OUTER JOIN emp ON dept.id = emp.dept_id GROUP BY dept.dname;
-- 3.后续的查询

SELECT 
  dept.`id` AS 部门编号,
  dept.`dname` AS 部门名称,
  dept.`loc` AS 部门位置,
  COUNT(emp.`dept_id`) AS 部门人数 
FROM
  dept 
  LEFT OUTER JOIN emp 
    ON dept.`id` = emp.`dept_id` 
GROUP BY dept.`dname` ;

-- 练习5
-- 列出所有员工的姓名及其直接上级领导的姓名, 没有上级领导的员工也需要显示,显示自己的名字和领导的名字
-- 1.根据需求明确查询哪些表 emp pt emp ld 表自连
SELECT * FROM emp pt INNER JOIN emp ld;
-- SELECT * FROM emp INNER JOIN emp; -- Not unique table/alias: 'emp'
-- 2.明确表连接条件去掉笛卡尔积
SELECT * FROM emp pt LEFT OUTER JOIN emp ld ON pt.mgr
-- 3.后续的查询

SELECT 
pt.`ename` AS 员工姓名,
ld.`ename` AS 领导姓名 
FROM 
emp pt 
LEFT OUTER JOIN emp ld ON pt.`mgr` = ld.`id`;

-- 子查询
SELECT * FROM emp;
SELECT 
pt.`ename` AS 员工姓名,
emp.`ename` AS 领导姓名  
FROM (SELECT * FROM emp) pt 
LEFT OUTER JOIN emp ON pt.mgr = emp.id;