SQL Server-使用分组依据时，如何在Select语句中具有未聚合的列？

Question

I want the MAX(Date) for each distinct ID. This is easy:

SELECT
    Id,
    MAX(LastModifiedDate)
FROM 
    [MyServer].[Database].[Table]
GROUP BY
    Id;

but I also need to include other columns like first name, last name, company, etc. which cannot be aggregated, and it won't work if I put them in the GROUP BY clause, because then it returns rows I don't want.

Answer 1

In order to do this, instead of using group by, try over():

select Id, <any other thing you want>,max(LastModifiedDate) over (partition by Id) as LastModifiedDate
FROM [MyServer].[Database].[Table]; 

Answer 2

Use that query to filter with the same table by ID and that last modified date.

SELECT
    T.*
FROM
    [MyServer].[Database].[Table] AS T
    INNER JOIN (
        select Id,
        MAX(LastModifiedDate) AS  MaxLastModifiedDate
        FROM [MyServer].[Database].[Table]
        group by Id
    ) AS N ON 
        T.Id = N.Id AND
        N.MaxLastModifiedDate = T.LastModifiedDate

---

EDIT : If you have multiple max dates for each ID, then you can't use their value to filter. You can use a ROW_NUMBER to rank them instead:

;WITH MaxByRowNumber AS
(
    SELECT
        T.*,
        LastModifiedDateRanking = ROW_NUMBER() OVER (PARTITION BY T.ID ORDER BY T.LastModifiedDate DESC)
    FROM 
        [MyServer].[Database].[Table] AS T
)
SELECT
    M.*
FROM
    MaxByRowNumber AS M
WHERE
    M.LastModifiedDateRanking = 1

You might want to add another column to the ORDER BY to untie the most recent updated dates, or not, depending on your needs.

Answer 3

One way would be using a CTE :

with cte as 
(
  select Id,
  max(LastModifiedDate) LastModifiedDate
  FROM [MyServer].[Database].[Table]
  group by Id
)
select t.*, c.LastModifiedDate
from [MyServer].[Database].[Table] t join cte c on t1.id = cte.id

Answer 4

Figured this out literally as soon as I posted it. I was just confused on the proper way to use a window function.

SELECT [Id]
  ,LastModifiedDate
  ,Row_Number() over (Partition by Id order by LastModifiedDate DESC) as rn
  ,[FirstName]
  ,[LastName]
  ,[Company]
  ,[Title]     
FROM [MyServer].[Database].[Table] as C
where rn = 1

What i was trying to do was:

,Row_Number() over (Partition by Id order by MAX(LastModifiedDate) DESC) as rn

but MAX makes no sense because it is DESC

Answer 5

You can use subquery :

select t.*
from table t
where LastModifiedDate = (select max(t1.LastModifiedDate) 
                          from table t1 
                          where t1.id = t.id
                         );