# 查询所有数据库
show databases ;

#切换数据库
use db01;

#查询当前使用的数据库
select database();

#创建数据库
create database db03;

#删除数据库
drop database db03;

# -------------------------->表操作<---------------------
#创建表
create table user(
    id int comment 'ID 唯一',
    username varchar(50) comment '用户名',
    name varchar(10) comment '姓名',
    age int comment '年龄',
    gender char(1) comment '性别'
)comment '用户表';

#删除表
drop table user;

#创建约束表
create table user(
    id int unsigned primary key auto_increment comment 'ID 唯一', -- 主键约束
    username varchar(50) not null unique comment '用户名', -- 唯一非空约束
    name varchar(10) not null comment '姓名', -- 非空约束
    age tinyint unsigned comment '年龄',
    gender char(1) default '男' comment '性别'
)comment '用户表';


# 案例：设计员工表 emp
create table emp(
    id int unsigned primary key auto_increment comment 'ID 唯一',
    username varchar(20) not null unique comment '用户名', -- 唯一非空约束
    password varchar(20) not null default '123456' comment '密码',
    name varchar(10) not null comment '姓名',
    gender tinyint unsigned not null default 1 comment '性别: 1男 2女', -- 修改为数值默认值
    phone char(11) not null comment '手机号',
    job tinyint unsigned comment '职位: 1班主任 2讲师 3学生主管 4教研主管 5咨询师',
    salary int unsigned comment '薪资',
    entry_date date comment '入职时间',
    image varchar(255) comment '图像',
    create_time timestamp comment '创建时间',
    update_time timestamp comment '更新时间'
)comment '员工表';



# -------------------------->数据操作<---------------------
#查询当前所有表
show tables;

#查看表结构
describe emp;

#查询建表语句
show create table emp;

#添加字段 qq varchar(13)
alter table emp add qq varchar(13) comment 'QQ';

#修改字段 qq varchar(13) -> varchar(15)
alter table emp modify qq varchar(15) comment 'QQ';

#修改字段名 qq -> qq_num
alter table emp change qq qq_num varchar(15) comment 'QQ';

#删除字段 qq_num
alter table emp drop qq_num;

#修改表名
alter table emp rename to employee;

#删除表
drop table employee;



# -------------------------->DML<---------------------

-- DML : 数据操作语言
-- DML : 插入数据 - insert
-- 1. 为 emp 表的 username, password, name, gender, phone 字段插入值
insert into emp(username, password, name, gender, phone) values('songjiang', '12345678', '宋江', 1, '13888888888');

insert into emp(username, password, name, gender, phone) values('songjiang2', '12345678', '宋江', 1, '13888888888');

-- 2. 为 emp 表的 所有字段插入值
#方式一
insert  into emp(id, username, password, name, gender, phone, job, salary, entry_date, image, create_time, update_time)
    values (null, 'linchong', '12345678', '林冲', 1, '13888888882', 1, 6000, '2020-01-01', '1.jpg', now(), now());
#方式二
insert into emp values(null, 'likui', '12345678', '李逵', 1, '13888888883', 1, 6000, '2020-01-01', '1.jpg', now(), now());
-- 3. 批量为 emp 表的 username, password, name, gender, phone  字段插入数据
insert into emp(username, password, name, gender, phone) values
    ('lisi', '12345678', '李四', 1, '13888888884'),
    ('wangwu', '12345678', '王五', 1, '13888888885'),
    ('zhaoliu', '12345678', '赵六', 1, '13888888886'),
    ('tianqi', '12345678', '田七', 1, '13888888887');

-- DML : 更新数据 - update
-- 1. 将 emp 表的ID为1员工 用户名更新为 'zhangsan', 姓名name字段更新为 '张三'
update emp set username = 'zhangsan', name = '张三' where id = 1;

-- 2. 将 emp 表的所有员工的入职日期更新为 '2010-01-01'
update emp set entry_date = '2010-01-01';



-- DML : 删除数据 - delete
-- 1. 删除 emp 表中 ID为1的员工
delete from emp where id = 1;

-- 2. 删除 emp 表中的所有员工
delete from emp;



-- 准备测试数据
INSERT INTO emp(id, username, password, name, gender, phone, job, salary, image, entry_date, create_time, update_time)
VALUES (1,'shinaian','123456','施耐庵',1,'13309090001',4,15000,'1.jpg','2000-01-01','2024-04-11 16:35:33','2024-04-11 16:35:35'),
     (2,'songjiang','123456','宋江',1,'13309090002',2,8600,'2.jpg','2015-01-01','2024-04-11 16:35:33','2024-04-11 16:35:37'),
     (3,'lujunyi','123456','卢俊义',1,'13309090003',2,8900,'3.jpg','2008-05-01','2024-04-11 16:35:33','2024-04-11 16:35:39'),
     (4,'wuyong','123456','吴用',1,'13309090004',2,9200,'4.jpg','2007-01-01','2024-04-11 16:35:33','2024-04-11 16:35:41'),
     (5,'gongsunsheng','123456','公孙胜',1,'13309090005',2,9500,'5.jpg','2012-12-05','2024-04-11 16:35:33','2024-04-11 16:35:43'),
     (6,'huosanniang','123456','扈三娘',2,'13309090006',3,6500,'6.jpg','2013-09-05','2024-04-11 16:35:33','2024-04-11 16:35:45'),
     (7,'chaijin','123456','柴进',1,'13309090007',1,4700,'7.jpg','2005-08-01','2024-04-11 16:35:33','2024-04-11 16:35:47'),
     (8,'likui','123456','李逵',1,'13309090008',1,4800,'8.jpg','2014-11-09','2024-04-11 16:35:33','2024-04-11 16:35:49'),
     (9,'wusong','123456','武松',1,'13309090009',1,4900,'9.jpg','2011-03-11','2024-04-11 16:35:33','2024-04-11 16:35:51'),
     (10,'lichong','123456','林冲',1,'13309090010',1,5000,'10.jpg','2013-09-05','2024-04-11 16:35:33','2024-04-11 16:35:53'),
     (11,'huyanzhuo','123456','呼延灼',1,'13309090011',2,9700,'11.jpg','2007-02-01','2024-04-11 16:35:33','2024-04-11 16:35:55'),
     (12,'xiaoliguang','123456','小李广',1,'13309090012',2,10000,'12.jpg','2008-08-18','2024-04-11 16:35:33','2024-04-11 16:35:57'),
     (13,'yangzhi','123456','杨志',1,'13309090013',1,5300,'13.jpg','2012-11-01','2024-04-11 16:35:33','2024-04-11 16:35:59'),
     (14,'shijin','123456','史进',1,'13309090014',2,10600,'14.jpg','2002-08-01','2024-04-11 16:35:33','2024-04-11 16:36:01'),
     (15,'sunerniang','123456','孙二娘',2,'13309090015',2,10900,'15.jpg','2011-05-01','2024-04-11 16:35:33','2024-04-11 16:36:03'),
     (16,'luzhishen','123456','鲁智深',1,'13309090016',2,9600,'16.jpg','2010-01-01','2024-04-11 16:35:33','2024-04-11 16:36:05'),
     (17,'liying','12345678','李应',1,'13309090017',1,5800,'17.jpg','2015-03-21','2024-04-11 16:35:33','2024-04-11 16:36:07'),
     (18,'shiqian','123456','时迁',1,'13309090018',2,10200,'18.jpg','2015-01-01','2024-04-11 16:35:33','2024-04-11 16:36:09'),
     (19,'gudasao','123456','顾大嫂',2,'13309090019',2,10500,'19.jpg','2008-01-01','2024-04-11 16:35:33','2024-04-11 16:36:11'),
     (20,'ruanxiaoer','123456','阮小二',1,'13309090020',2,10800,'20.jpg','2018-01-01','2024-04-11 16:35:33','2024-04-11 16:36:13'),
     (21,'ruanxiaowu','123456','阮小五',1,'13309090021',5,5200,'21.jpg','2015-01-01','2024-04-11 16:35:33','2024-04-11 16:36:15'),
     (22,'ruanxiaoqi','123456','阮小七',1,'13309090022',5,5500,'22.jpg','2016-01-01','2024-04-11 16:35:33','2024-04-11 16:36:17'),
     (23,'ruanji','123456','阮籍',1,'13309090023',5,5800,'23.jpg','2012-01-01','2024-04-11 16:35:33','2024-04-11 16:36:19'),
     (24,'tongwei','123456','童威',1,'13309090024',5,5000,'24.jpg','2006-01-01','2024-04-11 16:35:33','2024-04-11 16:36:21'),
     (25,'tongmeng','123456','童猛',1,'13309090025',5,4800,'25.jpg','2002-01-01','2024-04-11 16:35:33','2024-04-11 16:36:23'),
     (26,'yanshun','123456','燕顺',1,'13309090026',5,5400,'26.jpg','2011-01-01','2024-04-11 16:35:33','2024-04-11 16:36:25'),
     (27,'lijun','123456','李俊',1,'13309090027',5,6600,'27.jpg','2004-01-01','2024-04-11 16:35:33','2024-04-11 16:36:27'),
     (28,'lizhong','123456','李忠',1,'13309090028',5,5000,'28.jpg','2007-01-01','2024-04-11 16:35:33','2024-04-11 16:36:29'),
     (29,'songqing','123456','宋清',1,'13309090029',5,5100,'29.jpg','2020-01-01','2024-04-11 16:35:33','2024-04-11 16:36:31'),
     (30,'liyun','123456','李云',1,'13309090030',NULL,NULL,'30.jpg','2020-03-01','2024-04-11 16:35:33','2024-04-11 16:36:31');






--  =================== DQL: 基本查询 ======================
-- 1. 查询指定字段 name,entry_date 并返回
select name, entry_date from emp;


-- 2. 查询返回所有字段
#方式一：不推荐
select * from emp;
#方式二：推荐
select id, username, password, name, gender, phone, job, salary, image, entry_date, create_time, update_time from emp;

-- 3. 查询所有员工的 name,entry_date, 并起别名(姓名、入职日期)
select name as 姓名, entry_date as 入职日期 from emp;
select name as 姓名, emp.entry_date as 入职日期 from emp;
select name 姓名, emp.entry_date 入职日期 from emp;

-- 4. 查询已有的员工关联了哪几种职位(不要重复) --distinct 去除重复
select distinct job from emp;


--  =================== DQL: 条件查询 ======================
-- 1. 查询 姓名 为 柴进 的员工
select * from emp where name = '柴进';
select * from emp where name = '柴进';

-- 2. 查询 薪资小于等于5000 的员工信息
select * from emp where salary <= 5000;
select * from emp where salary <= 5000;

-- 3. 查询 没有分配职位 的员工信息
select * from emp where job is null;


-- 4. 查询 有职位 的员工信息
select * from emp where job is not null;


-- 5. 查询 密码不等于 '123456' 的员工信息
select * from emp where password != '123456';


-- 6. 查询 入职日期 在 '2000-01-01' (包含) 到 '2010-01-01'(包含) 之间的员工信息\
select * from emp where entry_date >= '2000-01-01' and entry_date <= '2010-01-01';


-- 7. 查询 入职时间 在 '2000-01-01' (包含) 到 '2010-01-01'(包含) 之间 且 性别为女 的员工信息
select * from emp where entry_date >= '2000-01-01' and entry_date <= '2010-01-01' and gender = 2;

-- 8. 查询 职位是 2 (讲师), 3 (学工主管), 4 (教研主管) 的员工信息
select * from emp where job in (2,3,4);
select * from emp where job = 2 or job = 3 or job = 4;


-- 9. 查询 姓名 为两个字的员工信息
select * from emp where name like '__';


-- 10. 查询 姓 '李' 的员工信息
select * from emp where name like '李%';


-- 11. 查询 姓名中包含 '二' 的员工信息
select * from emp where name like '%二%';



--  =================== DQL: 分组查询 ======================
-- 聚合函数
-- 所有null不参与计数
-- 1. 统计该企业员工数量
-- cont(字段)
select count(id) from emp;

-- cont(*) 推荐
select count(*) from emp;

-- cont(常量)
select count(123) from emp;

-- 2. 统计该企业员工的平均薪资
select avg(salary) from emp;


-- 3. 统计该企业员工的最低薪资
select min(salary) from emp;


-- 4. 统计该企业员工的最高薪资
select max(salary) from emp;


-- 5. 统计该企业每月要给员工发放的薪资总额(薪资之和)
select sum(salary) from emp;





-- 分组
-- 1. 根据性别分组 , 统计男性和女性员工的数量
select gender 性别, count(*) 数量 from emp group by gender;
select gender, count(*) from emp group by gender;


-- 2. 先查询入职时间在 '2015-01-01' (包含) 以前的员工 , 并对结果根据职位分组 , 获取员工数量大于等于2的职位
select job, count(*) from emp where entry_date <= '2015-01-01' group by job having count(*) >= 2;



--  =================== 排序查询 ======================
-- 1. 根据入职时间, 对员工进行升序排序
select * from emp order by entry_date;
select * from emp order by entry_date asc;


-- 2. 根据入职时间, 对员工进行降序排序
select * from emp order by entry_date desc;

-- 3. 根据 入职时间 对公司的员工进行 升序排序 ， 入职时间相同 , 再按照 更新时间 进行降序排序
select * from emp order by entry_date asc, update_time desc;




--  =================== 分页查询 ======================
-- 1. 从起始索引0开始查询员工数据, 每页展示5条记录
select * from emp limit 0,5;

-- 2. 查询 第1页 员工数据, 每页展示5条记录
select * from emp limit 0,5;

-- 3. 查询 第2页 员工数据, 每页展示5条记录
select * from emp limit 5,5;

-- 4. 查询 第3页 员工数据, 每页展示5条记录
select * from emp limit 10,5;