--學生成績表(姓名，科目，分數）
create table studentscores
(
id uniqueidentifier not null primary key default newid()
,name nvarchar(36)
,subject nvarchar(36)
,scores decimal(14,1)
)
insert into studentscores(name,subject,scores) values('張三','語文',59)
insert into studentscores(name,subject,scores) values('張三','數學',80)
insert into studentscores(name,subject,scores) values('張三','英語',100)
insert into studentscores(name,subject,scores) values('張三','語文',65)--補考
insert into studentscores(name,subject,scores) values('李四','語文',76)
insert into studentscores(name,subject,scores) values('李四','數學',56)
insert into studentscores(name,subject,scores) values('李四','英語',80)
insert into studentscores(name,subject,scores) values('李四','數學',60)--補考
insert into studentscores(name,subject,scores) values('王五','語文',96)
insert into studentscores(name,subject,scores) values('王五','數學',85)
insert into studentscores(name,subject,scores) values('王五','英語',64)
--取每個人各門功課最好成績，row_number()按name,subject分組，scores由高到低
select id,name,subject,scores from(
select
id,name,subject,scores
,row_number() over(partition by name,subject order by scores desc) num
from studentscores
)t
where num=1
--取各科目成績排名前2的記錄
select id,name,subject,scores from(
select
id,name,subject,scores
,row_number() over(partition by subject order by scores desc) num
from studentscores
)t
where num<=2
order by subject,scores desc
--保留每個人各科目最高分的記錄，刪除其它記錄
delete studentscores where id
in(
select id from(
select id
,row_number() over(partition by name,subject order by scores desc) num
from studentscores)t1
where num<>1
)
drop table studentscores;