MySql exercise 2

MySql exercise 2

One

1. Query the subjects with the highest scores for each student (required to display fields: student ID, name, course, highest score)
2. Query the students with the best grades in each course (required to display fields: student ID, name, subject, grade)

-- 1. 查询出每个学生最高成绩的科目(要求显示字段: 学号，姓名，课程，最高成绩)
SELECT stud.stu_num,stud.stu_name,stud.subject,stu_score
FROM(SELECT stu_num,MAX(stu_score) AS maxScore
  FROM stud
  GROUP BY stu_num) t2
  JOIN stud
    ON stud.stu_num = t2.stu_num
    AND stud.stu_score = t2.maxScore

-- 2. 查询各门课程成绩最好的学生(要求显示字段: 学号，姓名，科目，成绩) 
SELECT stud.stu_num,stud.stu_name,stud.subject,stu_score
FROM(SELECT SUBJECT,MAX(stu_score) AS maxScore
  FROM stud
  GROUP BY SUBJECT) t2
  JOIN stud
    ON stud.SUBJECT = t2.SUBJECT
    AND stud.stu_score = t2.maxScore

2. There are two tables

Department table,

employee table,

two tables related query

1. Query all employee information, the information content includes
   employee primary key, employee name, gender, age, salary, and department name
2. Query the employee with the highest salary, and display the employee information, and query the highest salary from the query
3. Query the information of the employee with the highest salary in each department
4. Query the total wages, average wages, maximum wages, and minimum wages of all male employees
5. Query information about employees whose salary is greater than the average salary
6. Query the name and gender of all employees surnamed Wang
7. Query the names and ages of the top 3 oldest employees
8. Count the sum of salary of each department, display information: department name, sum of salary,
   first associate the employee table with the department table. Group by department
9. Count the total number of people in each department, display information: department name, department number

CREATE TABLE part(
	id INT PRIMARY KEY AUTO_INCREMENT,
	Dept_name VARCHAR(20),
	Dept_Desc VARCHAR(20),
	Dept_date DATE
)
INSERT INTO part(id,Dept_name,Dept_Desc,Dept_date)
	    VALUES(1,'研发部','开发软件','2014-12-14'),
		  (2,'财务部','发工资','2014-10-14'),
		  (3,'市场部','销售软件','2015-11-02')
CREATE TABLE people(
	id INT PRIMARY KEY AUTO_INCREMENT,
	NAME VARCHAR(20),
	sex CHAR(1) CHECK(sex='男' OR sex = '女'),
	age INT,
	money INT,
	Dept_id VARCHAR(20)
)
INSERT INTO people(NAME,sex,age,money,Dept_id)
	    VALUES('王五','男',25,3000,1),
	    ('李明','男',23,2500,1),
	    ('王二小','男',23,2356,2),
	    ('陈发','男',22,3600,2),
	    ('小明','男',21,3100,3),
	    ('苏奇','男',24,2800,3),
	    ('王丽','女',19,1800,1),
	    ('李芳','女',18,1900,3)
-- 1.	查询所有员工信息，信息内容包括员工主键，员工姓名，性别，年龄，工资，所属部门名称
SELECT *
FROM people
-- 2.	查询出工资最高的员工，并显示员工信息  自查询 查询出最高工资
SELECT * 
FROM people p1,(SELECT MAX(money) maxmoney
FROM people) p2
WHERE p1.money = p2.maxmoney

-- 3.	查询出每个部门工资最高的员工信息
SELECT * 
FROM people p1,(SELECT Dept_id, MAX(money) maxmoney
FROM people GROUP BY Dept_id) p2
WHERE p1.money = p2.maxmoney AND p1.Dept_id = p2.Dept_id


-- 4.	查询所有男性员工工资总和,平均工资,最高工资,最低工资
SELECT SUM(money),AVG(money),MAX(money),MIN(money)
FROM people
WHERE id NOT IN (SELECT id
          FROM people
          WHERE sex='女')


-- 5.	查询工资大于平均工资的员工信息
SELECT *
FROM people p1 ,(SELECT AVG(money) avgm
FROM people) p2
WHERE p1.money > p2.avgm

-- 6.	查询所有姓王员工的姓名和性别
SELECT NAME,sex
FROM people
WHERE NAME LIKE '王%'

-- 7.	查询年龄最大的前3个员工的姓名和年龄
SELECT *
FROM people
ORDER BY age DESC
LIMIT 3

-- 8.	统计每个部门的工资总和,显示信息：部门名称，工资总和 
-- 首先用员工表与部门表关联.用部门分组
SELECT Dept_name,工资总和
FROM part t , (SELECT SUM(money) 工资总和,Dept_id FROM people GROUP BY Dept_id) p
WHERE t.id = p.Dept_id

-- 9.统计每个部门的总人数,显示信息：部门名称，部门人数
SELECT Dept_name,人数
FROM part t , (SELECT COUNT(id) 人数,Dept_id FROM people GROUP BY Dept_id) p
WHERE t.id = p.Dept_id