MySQL设计和多表操作

1. 约束的概念

约束是作用于表中列上的规则，用于限制加入表的数据

约束的存在保证了数据库中数据的正确性、有效性和完整性

外键约束

外键用来让两个表的数据之间建立链接，保证数据的一致性和完整性

数据库设计

DROP TABLE IF EXISTS dept;


# 创建部门表
	CREATE TABLE dept(
		did INT PRIMARY KEY AUTO_INCREMENT,
		dname VARCHAR(20)
	);
	
	DROP TABLE IF EXISTS emp;
	# 创建员工表
	CREATE TABLE emp (
		id INT PRIMARY KEY AUTO_INCREMENT,
		NAME VARCHAR(10),
		gender CHAR(1), -- 性别
		salary DOUBLE, -- 工资
		join_date DATE, -- 入职日期
		dep_id INT,
		FOREIGN KEY (dep_id) REFERENCES dept(did) -- 外键，关联部门表(部门表的主键)
	);
	-- 添加部门数据
	INSERT INTO dept (dNAME) VALUES ('研发部'),('市场部'),('财务部'),('销售部');
	-- 添加员工数据
	INSERT INTO emp(NAME,gender,salary,join_date,dep_id) VALUES
	('孙悟空','男',7200,'2013-02-24',1),
	('猪八戒','男',3600,'2010-12-02',2),
	('唐僧','男',9000,'2008-08-08',2),
	('白骨精','女',5000,'2015-10-07',3),
	('蜘蛛精','女',4500,'2011-03-14',1),
	('小白龙','男',2500,'2011-02-14',null);	


select * from emp;

-- 多表查询

select * from emp , dept;

-- 笛卡尔积 ： 有 A ,B两个集合 取 A,B所有的组合情况


-- 消除无效数据


-- 查询emp 和 dept 的数据 ，emp.dep_id = dept.did

select * from emp , dept where emp.dep_id = dept.did;

-- 查询 emp的 name， gender，dept表的dname
SELECT
	emp. NAME,
	emp.gender,
	dept.dname
FROM
	emp,
	dept
WHERE
	emp.dep_id = dept.did;

-- 给表 起别名
SELECT
	t1. NAME,
	t1.gender,
	t2.dname
FROM
	emp t1,
	dept t2
WHERE
	t1.dep_id = t2.did;


-- 显式内连接

select * from emp inner join dept on emp.dep_id = dept.did;

select * from emp  join dept on emp.dep_id = dept.did;

-- 左外连接
-- 查询emp表所有数据和对应的部门信息

select * from emp left join dept on emp.dep_id = dept.did;


-- 右外连接
-- 查询dept表所有数据和对应的员工信息

select * from emp right join dept on emp.dep_id = dept.did;


select * from dept left join emp on emp.dep_id = dept.did;

-- 查询工资高于猪八戒的员工信息

select * from emp;
select * from dept;

select * from emp where salary > (select salary from emp where name = '猪八戒' )

-- 查询 '财务部' 和 '市场部' 所有的员工信息
-- 查询 '财务部' 所有的员工信息

select * from emp where dep_id in (select did from dept where dname = '财务部' or dname = '市场部');
select * from emp where dep_id  = (select did from dept where dname = '财务部');

-- 查询入职日期是 '2011-11-11' 之后的员工信息和部门信息
-- 查询入职日期是 '2011-11-11' 之后的员工信息

select * from emp where join_date > '2011-11-11' ;


select * from (select * from emp where join_date > '2011-11-11' ) t1, dept where t1.dep_id = dept.did;

案例练习

DROP TABLE IF EXISTS emp;
DROP TABLE IF EXISTS dept;
DROP TABLE IF EXISTS job;
DROP TABLE IF EXISTS salarygrade;


-- 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
);



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

-- 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)
);
-- 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');

-- 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');


-- 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);


-- 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);

SELECT * FROM job
SELECT * from emp
select * from dept
select * from salarygrade

-- 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 e1.dept_id,e1.ename,e1.salary, j1.jname,j1.description from emp e1,job j1  where e1.job_id = j1.id
-- 显式内连接
SELECT
	emp.id,
	emp.ename,
	emp.salary,
	job.jname,
	job.description
FROM
	emp
INNER JOIN job ON 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 e1.dept_id,e1.ename,e1.salary, j1.jname,j1.description,d.dname,d.loc from emp e1,job j1,dept d  where e1.job_id = j1.id and  e1.dept_id = d.id;

-- 显式内连接
SELECT
	emp.id,
	emp.ename,
	emp.salary,
	job.jname,
	job.description,
	dept.dname,
	dept.loc
FROM
	emp
INNER JOIN job ON emp.job_id = job.id
INNER JOIN dept ON dept.id = emp.dept_id
-- 3.查询员工姓名，工资，工资等级
SELECT e.ename,e.salary,s.grade FROM emp e,salarygrade s WHERE e.salary >= s.losalary and e.salary <= s.hisalary;

SELECT
	emp.ename,
	emp.salary,
	t2.*
FROM
	emp,
	salarygrade t2
WHERE
	emp.salary >= t2.losalary
AND emp.salary <= 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.id,
	emp.ename,
	emp.salary,
	job.jname,
	job.description,
	dept.dname,
	dept.loc,
	t2.grade
FROM
	emp
INNER JOIN job ON emp.job_id = job.id
INNER JOIN dept ON dept.id = emp.dept_id
INNER JOIN salarygrade t2 ON emp.salary BETWEEN t2.losalary and t2.hisalary;

-- 5.查询出部门编号、部门名称、部门位置、部门人数
SELECT
	dept.id,
	dept.dname,
	dept.loc,
	t1.count
FROM
	dept,
	(
		SELECT
			dept_id,
			count(*) count
		FROM
			emp
		GROUP BY
			dept_id
	) t1
WHERE
	dept.id = t1.dept_id