Question

I have a table with three columns

UserID, Count, Date

I’d like to be able to select the userid with the highest count for each date.

I’ve tried a few different variations of queries with inline select statements but none have worked 100%, and I’m not too fond of having a select with three inline selects.

Is doing inline selects the only way to go without using temp tables? Whats the best way to tackle this?

Answer 1

If [Date] is in fact a [Date] column with no time component:

;WITH x AS
(
  SELECT [Date], [Count], UserID, rn = ROW_NUMBER() OVER
    (PARTITION BY [Date] ORDER BY [Count] DESC)
    FROM dbo.table
)
SELECT [Date], [Count], UserID
FROM x
WHERE rn = 1
ORDER BY [Date];

If [Date] is a DATETIME column with a time component, then:

;WITH x AS
(
  SELECT [Date] = DATEADD(DAY, DATEDIFF(DAY, '19000101', [Date]), '19000101'), 
    [Count], UserID, rn = ROW_NUMBER() OVER
    (PARTITION BY DATEADD(DAY, DATEDIFF(DAY, '19000101', [Date]), '19000101')
       ORDER BY [Count] DESC)
    FROM dbo.table
)
SELECT [Date], [Count], UserID
FROM x
WHERE rn = 1
ORDER BY [Date];

If you want to pick a specific row in the event of a tie, you can add a tie-breaker to the ORDER BY within the over. If you want to include multiple rows in the case of ties, you can try changing ROW_NUMBER() to DENSE_RANK().