sql-server - MS SQL 查询以显示最大重复列的 id

Question

我有一张桌子

tbl疾病追踪

TrackID 疾病 ID 邮政编码
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

我想写一个查询来显示每个邮政编码的疾病ID和最大重复疾病ID的邮政编码，如下所示，

疾病 ID 邮政编码
3 111
1 222
5 333

请任何帮助将不胜感激。我尝试了一切，但找不到任何帮助..再次感谢您:)

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

这将返回您想要的内容：

DiseaseID  PostalCode 
3          111
1          222
5          333

---

编辑：

与上面相同的查询，但使用 JOIN 从第二个表中获取城市名称：

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

请注意，我PostalCode在 city 表中也使用了相同的列名，因此我必须在最外面的查询中添加 PostalCode 前缀：T2.postalcode而不是postalcode.

否则查询会因以下消息而崩溃：

不明确的列名“邮政编码”

...因为 SQL Server 不知道我想要两个 PostalCode 中的哪一个。