SQL分组后取topN

news2024/10/6 1:44:15

准备数据

create table SC(
SId varchar(10) comment "学生ID",
CId varchar(10) comment "课程ID",
score decimal(18,1) comment "课程成绩");

insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

1、TOP 1

求每门课程中成绩最好的人

使用窗口函数:

SELECT SId ,CId,score from (
SELECT SId,CId,score,dense_rank() over (partition by CId ORDER BY score desc) as ranking from sc ) new 
where ranking=1

2、TOP N

求每门课程成绩前两人

使用窗口函数:

SELECT SId,CId,score from (
SELECT SId,CId,score,rank() over (PARTITION by CId ORDER BY score DESC) as ranking
from sc ) b
where ranking<=2;

3、三种排名的方式

#这是代码
SELECT SId,CId,score,
row_number() over (partition by CId ORDER BY score desc) as row_number2,
rank() over (partition by CId ORDER BY score desc) as rank2,
dense_rank() over (partition by CId ORDER BY score desc) as dense_rank2
from sc
where CId = "01"；

这是对CID分组，按分数排名的表