编辑代码

-- CREATE DATABASE school;
-- use school;
-- CREATE TABLE students (
--     id INT PRIMARY KEY comment '编号',
--     name VARCHAR(50) comment '姓名',
--     age INT comment '年龄',
--     gerden VARCHAR(1) comment '性别'
-- );

-- INSERT INTO students(id,name,age,gerden) 
-- VALUES (1,'小明',20,'男'),
--         (2,'小红',54,'女'),
--         (3,'小刚',23,'男');

-- alter table students add score INT;

-- alter table students change gerden gender varchar(1);

-- UPDATE students
-- SET score = 98
-- WHERE id = 1;

-- UPDATE students
-- SET score = 45
-- WHERE id = 2;

-- UPDATE students
-- SET score = 67
-- WHERE id = 3;

-- INSERT INTO students(id,name,age,gender,score) 
-- VALUES (4,'小赵',50,'男',78),
--         (5,'小光',24,'女',99);

-- UPDATE students SET name='小青', gender='女' WHERE id=4;

-- ALTER TABLE students add enterSchool DATE;
-- ALTER TABLE students add class varchar(10);

-- UPDATE students SET enterSchool = '2023-09-01';
-- UPDATE students SET class = '1班' WHERE id = 1;
-- UPDATE students SET class = '2班' WHERE id = 2;
-- UPDATE students SET class = '2班' WHERE id = 3;
-- UPDATE students SET class = '3班' WHERE id = 4;
-- UPDATE students SET class = '4班' WHERE id = 5;
-- select class AS '班级' from students;

CREATE DATABASE COMPUMENT;
use COMPUMENT;
CREATE TABLE emp(
    id INT PRIMARY KEY COMMENT '编号',
    workno VARCHAR(10) COMMENT '工号',
    name VARCHAR(10) COMMENT '姓名',
    gender CHAR(10) COMMENT '性别',
    age tinyint unsigned COMMENT '年龄',
    idcard CHAR(18) COMMENT '身份证号',
    workaddress VARCHAR(50) COMMENT '工作地址',
    entrydate DATE COMMENT '入职时间'
);

INSERT INTO emp (id,workno,name,gender,age,idcard,workaddress,entrydate)
VALUES (1,'1','柳岩','女',20,'123456789782738471','北京','2000-01-01'),
(2,'2','张无忌','男',45,'24234345362342312X','上海','2000-04-01'),
(3,'3','韦一名','男',40,'4673646736735','北京','2005-06-30'),
(4,'4','赵敏','女',25,'73365734323422','上海','2020-12-11'),
(5,'5','小昭','女',77,'34525666573673','上海','2023-03-21'),
(6,'6','逍遥','男',56,'4525633653345','北京','2012-04-04'),
(7,'7','范增','男',23,'3663673677367','北京','2013-06-05'),
(8,'8','黛绮丝','女',82,'87476836368463','上海','2012-08-21'),
(9,'9','范冰冰','女',13,'73735367337784566','上海','2003-02-12'),
(10,'10','陈友谅','男',53,'12312132145123414','上海','2005-09-03'),
(11,'11','张士诚','男',23,'3673767363X','北京','2006-10-06'),
(12,'12','常遇春','男',64,'7573667336573','北京','2007-11-12'),
(13,'13','张三丰','男',188,'3636567368','上海','2010-05-11'),
(14,'14','灭绝师太','女',77,'567783463686563','西安','2022-06-23'),
(15,'15','胡青牛','男',35,'3464683667837','上海','2021-07-26'),
(16,'16','周芷若','女',18,null,'上海','2015-02-08');


-- 1、查询指定字段name，workno，age返回
-- select name,workno,age from emp;

-- 2、查询所有字段返回
-- select id,workno,name,gender,age,idcard,workaddress,entrydate from emp;

-- 3、查询所有员工的工作地址，起别名
-- select workaddress AS '工作地址' from emp;

-- 4、查询所有员工的工作地址，起别名(不重复)
-- select distinct workaddress AS '工作地址' from emp;

-- 条件查询
-- 1、查询年龄等于82的员工
-- select * from emp
-- where age = 82;

-- 2、查询年龄小于20的员工信息
-- select * from emp
-- where age<20;

-- 3、查询年龄小于等于20的员工信息
-- select * from emp
-- where age<=20;

-- 4、查询没有身份证号的员工
-- select * from emp
-- where idcard is null;

-- 5、查询有身份证号的员工
-- select * from emp
-- where idcard is not null;

-- 6、查询查询年龄不等于82的员工
-- select * from emp
-- where age!=82;

-- 7、查询年龄在15岁(包含)到20岁(包含)之间的员工
-- select * from emp
-- where age>=15 and age <=20

-- select * from emp
-- where age between 15 and 20;

-- 8、查询性别为女且年龄小于25岁的员工
-- select * from emp
-- where gender='女'and age<25


-- 9、查询年龄等于18或20或40的；员工
-- select * from emp
-- where age=18 or age=20 or age=40;

-- select * from emp
-- where age in(18,20,40);

-- 10、查询姓名为两个字的员工信息
-- select * from emp
-- where name like '__';

-- 11、查询身份证号最后一位是X的员工信息
-- select * from emp
-- where idcard like '%X';

-- 聚合函数
-- 1、统计该企业员工的数量
-- select count(id) from emp;

-- 2、统计该企业员工的平均年龄
-- select avg(age) from emp;

-- 3、统计该企业员工的最大年龄
-- select max(age) from emp;

-- 4、统计该企业员工的最小年龄
-- select min(age) from emp;

-- 5、统计北京地区员工的年龄之和
-- select * from emp
-- where workaddress='北京';
-- select sum(age) from emp
-- where workaddress='北京';


-- 分组查询
-- 1、根据性别分组，统计男员工和女员工的数量
-- select gender,count(*) from emp
-- group by gender;

-- 2、根据性别分组，统计男员工和女员工的平均年龄
-- select gender,avg(age) from emp
-- group by gender;

-- 3、查询年龄小于45的员工，并根据工作地址分组，获取数量大于等于3的工作地址
-- select workaddress,count(*) address_count from emp
-- where age<45
-- group by workaddress
-- having address_count>=3;

-- 排序查询
-- 1、根据年龄对公司的员工进行升序排序
-- select name,age from emp
-- order by age;

-- select name,age from emp
-- order by age desc;

-- 2、根据入职时间，对员工进行降序排序
-- select name '姓名',entrydate '入职时间' from emp
-- order by entrydate desc;

-- 3、根据年龄对公司的员工进行升序排序，年龄相同，再按入职时间降序排序
-- select name,age,entrydate from emp
-- order by age asc,entrydate desc;

-- 分页查询
-- 1、查询第1页员工数据，每页展示10条记录
-- select * from emp
-- limit 0,10;

-- 2、查询第2页员工数据，每页展示10条记录
-- select * from emp
-- limit 10,10;

-- -- 1、查询年龄为20，21，22，23的女性员工信息
-- select * from emp
-- where age in (20,21,22,23) and gender='女';
-- -- 2、查询性别为男，并且年龄在20~40岁(含)以内的姓名为三个字的员工
-- select * from emp
-- where gender='男' and (age between 20 and 40 ) and name like '___';
-- -- 3、统计员工表中，年龄小于60岁的，男性员工和女性员工的人数
-- select gender,count(*) from emp
-- where age<60
-- group by gender;
-- -- 4、查询所有年龄小于等于35岁员工的姓名和年龄，并对查询结果按年龄升序排序，如果年龄相同按入职时间降序排序
-- select name,age from emp
-- where age<=35
-- order by age asc,entrydate desc;
-- -- 5、查询性别为男，且年龄在20-40岁(含)以内的前5个员工信息，对查询的结果按年龄升序排序，年龄相同按入职时间升序排序
-- select * from emp
-- where gender='男' and (age>=20 and age<=40)
-- order by age,entrydate
-- limit 5;

-- 查询年龄大于15的员工的姓名、年龄，并根据年龄进行升序排序
-- select name,age from emp
-- where age>15
-- order by age;

-- use mysql;
-- select * from user;

-- 创建用户itcast ，只能够在当前主机localhost访问，密码123456
-- create user 'itcast'@'localhost' identified by '123456';

-- 修改用户 itcast的访问密码为1234
-- alter user 'itcast'@'localhost' identified with mysql_native_password by '1234';

-- 删除用户
-- drop user 'itcast'@'localhost';

-- -- 查询权限
-- show grants for 'root'@'%';

-- -- 授予权限
-- grant all on itcast.* to 'root'@'%';

-- -- 撤销权限
-- revoke all on itcast.* from 'root'@'%';