项目管理软件开发案例,seo 资料包怎么获得,app制作教学课程,wordpress 添加友链学习笔记-SQL语法系统性学习#xff0c;关卡式进阶 笔记参考#xff1a;作者鱼皮 关卡式Sql语句学习体验网站 #xff0c;网站开源代码 如果想本地体验语法#xff1a;1.下载大佬开源代码#xff0c;运行前端项目#xff08;推荐#xff09;#xff1b; 2.或是自己使…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 student2、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dog7、基础语法 - 条件查询 - 空值 select name , age , score from student where age is not null8、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 50010、基础语法 - 去重 select distinct class_id , exam_num from student11、基础语法 - 排序 select name , age , score from student order by score desc , age asc12、基础语法 - 截断和偏移 select name , age from student order by age asc limit 1 , 313、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 student15、函数 - 字符串处理 select id , name , upper(name) as upper_name from student where name 热dog16、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 student17、分组聚合 - 单字段分组 select class_id , avg(score) as avg_score from student group by class_id18、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.id23、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_new26、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 student27、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 student28、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 student28、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 声明文章只供学习创造价值乐哉分享 一起入门后端 204146007