SQL ServerでROW_NUMBER（）を使用する方法

Question

Row_number（）は結果セットのパーティション内の行の連続番号を返します。各パーティションの最初の行は1から始まります。しかし、それは地下でどのように機能しますか？たとえば、ブックマークやインデックスを使用していますか？

よろしく

Answer 1

create table #test_rownumber 
(
name varchar(50) 
,score float 
,date_stamp varchar(20) 
) 

insert into #test_rownumber values('A',40,'2015-06-02') 
insert into #test_rownumber values('A',50,'2015-06-02') 
insert into #test_rownumber values('A',60,'2015-06-02') 
insert into #test_rownumber values('A',70,'2017-06-02') 
insert into #test_rownumber values('B',60,'2015-06-02') 
insert into #test_rownumber values('B',70,'2015-06-02') 
insert into #test_rownumber values('B',90,'2016-06-02') 
insert into #test_rownumber values('B',100,'2017-06-02') 


--you will see the row_number partion by name ,order by sore desc 
SELECT 
name 
,score 
,date_stamp 
,ROW_NUMBER() over(PARTITION by name order by score desc) as row_num 
from #test_rownumber 

--if you want to know the name and its' best score ,your may use that 
select 
name 
,score 
,date_stamp 
from(
SELECT 
name 
,score 
,date_stamp 
,ROW_NUMBER() over(PARTITION by name order by score desc) as row_num 
from #test_rownumber 
) a 
where row_num=1