SQL语法系统性学习，关卡式进阶-学习笔记

学习笔记-SQL语法系统性学习，关卡式进阶

笔记参考：作者鱼皮关卡式Sql语句学习体验网站，网站开源代码

如果想本地体验语法：1.下载大佬开源代码，运行前端项目（推荐）；
2.或是自己使用Sql工具，简单体验以下语法体验
使用MariaDB工具练习SQL语句教程

数据库建表

-- `student`
create table if not exists `student`
(`id`       integer          not null primary key AUTOINCREMENT,`name`     varchar(256)     not null,`age`      int              null,`class_id`    bigint           not null,`score`    double default 0 null,`exam_num` int    default 0 null
);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('鸡哥', 25, 1, 2.5, 1);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('鱼皮', 18, 1, 400, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('热dog', 40, 2, 600, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('摸FISH', null, 2, 360, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('李阿巴', 19, 3, 120, 2);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('老李', 56, 3, 500, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('李变量', 24, 4, 390, 3);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('王加瓦', 23, 4, 0, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('赵派森', 80, 4, 600, 4);
insert into `student` (`name`, `age`, `class_id`, `score`, `exam_num`)
values ('孙加加', 60, 5, 100.5, 1);

1、基础语法 - 查询 - 全表查询

select * from student

2、基础语法 - 查询 - 选择查询

select name, age from student;

3、基础语法 - 查询 - 别名

select name as 学生姓名, age as 学生年龄 from student;

4、基础语法 - 查询 - 常量和运算

select name , score, score * 2 as double_score from student;

5、基础语法 - 条件查询 - where

select name , score from student where name ='鱼皮'

6、基础语法 - 条件查询 - 运算符

select name , age from student where name != '热dog'

7、基础语法 - 条件查询 - 空值

select name , age , score from student where age is not null

8、基础语法 - 条件查询 - 模糊查询

select name , score from student where name not like '%李%'

9、基础语法 - 条件查询 - 逻辑运算

select name , score from  student where  name like '%李%' or score > 500

10、基础语法 - 去重

select distinct class_id , exam_num from student

11、基础语法 - 排序

select name , age , score from student order by score desc , age asc

12、基础语法 - 截断和偏移

select name , age from student order by age asc limit 1 , 3

13、基础语法 - 条件分支

select name , case when (age > 60) then '老同学'when (age >= 20) then '年轻' else  '小同学' end as age_level
from student order by name asc

14、函数 - 时间函数

select name , date() as 当前日期 from student

15、函数 - 字符串处理

select id ,  name , upper(name) as upper_name from student where  name = '热dog'

16、函数 - 聚合函数

select sum(score) as total_score , avg(score) as avg_score , max(score) as max_score, min(score)
as min_score from student

17、分组聚合 - 单字段分组

select class_id , avg(score) as avg_score from student group by class_id

18、分组聚合 - 多字段分组

select class_id ,exam_num, count (*) as total_num from student group by class_id ,exam_num

19、分组聚合 - having 子句


select class_id, sum(score) as total_score from student group by class_id having sum(score) > 150

20、查询进阶 - 关联查询 - cross join

select s.name as student_name , s.age as student_age,
s.class_id , c.name as class_name  from student s cross join class c;

21、查询进阶 - 关联查询 - inner join

select s.name as student_name , s.age as student_age , s.class_id ,
c.name as class_name, c.level as class_level from student s
join class c on s.class_id = c.id;

22、查询进阶 - 关联查询 - outer join

select s.name as student_name, s.age as student_age, s.class_id , c.name as class_name,
c.level as class_level from student s   left join class c on s.class_id = c.id

23、查询进阶 - 子查询

select name , score , class_id from student  where class_id
in (select id as class_id from class )

24、查询进阶 - 子查询 - exists

select name ,age , class_id from student
where not exists( select * from class where student.class_id = class.id)

24、查询进阶 - 组合查询


select name ,age ,score, class_id from student
union all
select name, age ,score, class_id from student_new

26、查询进阶 - 开窗函数 - sum over

开窗是一种强大的查询工具，它允许我们保留原始详细信息，且能进行对分组数据进行计算，拼接在每条数据上。像一个透视镜一样，能聚焦在特定分组展示了全部信息

select id , name , age, score, class_id ,
avg(score) over (partition by class_id) as  class_avg_score
from student

27、查询进阶 - 开窗函数 - sum over order by

累计求和

select id , name , age , score , class_id,
sum(score) over  (partition by class_id order by score asc) as class_sum_score
from student

28、查询进阶 - 开窗函数 - rank

select id , name , age , score , class_id ,
rank() over (partition by class_id order by score desc) as ranking
from student

28、查询进阶 - 开窗函数 - row_number

与rank的区别，行号唯一，相同也递增


select id , name , age , score , class_id,
row_number() over (partition by class_id order by score desc) as row_number
from student

30、查询进阶 - 开窗函数 - lag / lead

查看左/右情况

select id , name , age , score , class_id ,
lag(name ,1, null) over (partition by class_id order by score desc) as prev_name,
lead(name, 1,null) over (partition by class_id order by score desc) as next_name
from student