MS SQL查詢，以顯示最大重複列

Question

我有一個表的ID

 
tblDiseaseTrack 

TrackID DiseaseID PostalCode 
1  3   111 
2  3   111 
3  2   111 
4  1   222 
5  2   222 
6  4   111 
7  1   222 
8  5   333 
9  5   333 
10  5   333 

我想要寫一個查詢，顯示該疾病id和最大重複DiseaseId的每個郵遞區號郵政編碼如下，

 
DiseaseID PostalCode 
3   111 
1   222 
5   333 

請任何幫助將不勝感激。我想evrything和無法找到任何help..Thank你再次:)

Answer 1

select diseaseid, postalcode 
from 
(
    select 
     postalcode, 
     diseaseid, 
     row_number() over (partition by postalcode order by count desc) as row 
    from 
    (
     select postalcode, count(postalcode) as count, diseaseid 
     from tblDiseaseTrack 
     group by postalcode, diseaseid 
    ) as T1 
) as T2 
where row = 1 
order by postalcode 

這將返回你想要什麼：

DiseaseID PostalCode 
3   111 
1   222 
5   333 

---

編輯：

像同一查詢上面，但加入從第二個表中獲取城市名稱：

select diseaseid, T2.postalcode, city 
from 
(
    select 
     postalcode, 
     diseaseid, 
     row_number() over (partition by postalcode order by count desc) as row 
    from 
    (
     select postalcode, count(postalcode) as count, diseaseid 
     from @tblDiseaseTrack 
     group by postalcode, diseaseid 
    ) as T1 
) as T2 
inner join tblcity on T2.postalcode = tblcity.postalcode 
where row = 1 
order by postalcode 

請注意，我在城市表中使用了相同的列名PostalCode，所以我必須在最外面的查詢中加上PostalCode的前綴：T2.postalcode而不是postalcode。

否則查詢將與消息崩潰：

不明確的列名「郵編」

...因爲SQL Server不知道，我想這兩個PostalCodes的。