关于MySQL的几道小题

-- 1.创建一个t_user表的，字段为id(自增主键) name(用户名) age(年龄) sex(性别)

-- 2.向表中插入数据
-- name = 张三丰, age = 124 sex = 男
-- name = 张无忌, age = 18 sex = 男
-- name = 李四, age = 33 sex = 男
-- name = 赵六，age = 20 sex = 女
INSERT INTO t_user VALUES (null,'张三丰',124,'男'),(null,'张无忌',18,'男'),(null,'李四',33,'男'),(null,'赵六',20,'女');

-- 3.把姓名的赵六的人的年龄改成60岁
UPDATE t_user SET age=60 WHERE name='赵六';

-- 4.查询出所有姓张的人的个数
SELECT COUNT(*) FROM t_user WHERE name LIKE '张%';

-- 5.删除所有年龄大于30岁的男生
DELETE FROM t_user WHERE age>30;

CREATE TABLE student (
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20),
score DOUBLE,
sex VARCHAR(1)
)

INSERT INTO student VALUES ( NULL,'张三1',60,'男');
INSERT INTO student VALUES ( NULL,'张三2',70,'女');
INSERT INTO student VALUES ( NULL,'张三3',77,'女');
INSERT INTO student VALUES ( NULL,'张三4',80,'男');
INSERT INTO student VALUES ( NULL,'张三5',90,'男');
INSERT INTO student VALUES ( NULL,'张三6',100,'女');
INSERT INTO student VALUES ( NULL,'张三7',65,'男');
INSERT INTO student VALUES ( NULL,'张三8',68,'女');
INSERT INTO student VALUES ( NULL,'张三9',74,'男');

INSERT INTO student VALUES ( NULL,'张三11',90,'中');
INSERT INTO student VALUES ( NULL,'张三12',NULL,'中');
INSERT INTO student VALUES ( NULL,'张三13',60,'中');

-- 按照性别分组。分别查询男、女同学的平均分 --
SELECT sex,AVG(score) FROM student GROUP BY sex;

-- 按照性别分组。分别查询男、女同学的平均分,人数 --
SELECT sex,AVG(score),COUNT(*) AS 人数 FROM student GROUP BY sex;

-- 按照性别分组。分别查询男、女同学的平均分,人数 要求：分数低于70分的人，不参与分组 --
SELECT sex,AVG(score),COUNT(*) AS 人数 FROM student1 WHERE score>70 GROUP BY sex ;

-- 按照性别分组。分别查询男、女同学的平均分,人数 要求：分数低于70分的人，不参与分组,分组之后。人数要大于2个人 --
SELECT sex,AVG(score) AS 平均分,COUNT(*) AS 人数 FROM student1 WHERE score>70 GROUP BY sex HAVING COUNT(*)>=2;

-- 获取数据中的前5条数据 --
SELECT * FROM student LIMIT 0,5;

-- 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 e.id,ename,salary,jname,description FROM job j,emp e WHERE j.id=e.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 e.id,ename,salary,jname,description,dname,loc FROM job j,emp e,dept d WHERE j.id=e.job_id and d.id=e.dept_id;

-- 3.查询员工姓名，工资，工资等级
SELECT ename,salary,grade FROM emp e,salarygrade s WHERE e.salary BETWEEN s.losalary and s.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 ename,salary,jname,description,dname,loc,grade FROM job j,emp e,dept d,salarygrade s WHERE j.id=e.job_id and d.id=e.dept_id and e.salary BETWEEN s.losalary and s.hisalary;

-- 5.查询出部门编号、部门名称、部门位置、部门人数
SELECT d.id,d.dname,d.loc,COUNT(*) FROM dept d,emp e WHERE d.id=e.dept_id GROUP BY d.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 e1.ename AS 员工,e2.ename AS 领导 from emp e1 LEFT JOIN emp e2 ON e1.mgr=e2.id;

-- 7.查询部门人数大于3人的部门平均工资
SELECT AVG(salary) FROM dept d,emp e WHERE d.id=e.dept_id GROUP BY d.id HAVING COUNT(*)>3;

-- 8.查询出工资最高的人的姓名以及所属部门
SELECT e.ename,d.dname FROM emp e,dept d where d.id=e.dept_id and e.salary=(SELECT MAX(salary) FROM emp)

-- 9.查询出工资等级为5的员工的姓名以及职务名称
SELECT e.ename,j.description FROM emp e,job j,salarygrade s WHERE j.id=e.job_id AND e.salary BETWEEN s.losalary and s.hisalary and s.grade=5;