Utilizzare l'opzione con CTE , CROSS APPLICA operatore e ROW_NUMBER funzione di classifica
;WITH cte AS
(
SELECT [Date], Code
FROM dbo.YourTable
GROUP BY [Date], Code
)
SELECT c.Date, c.Code, o.Occurrences
FROM cte c
CROSS APPLY (
SELECT t2.[Date], t2.Code,
ROW_NUMBER() OVER(PARTITION BY c.[Date] ORDER BY t2.[Date]) AS Occurrences
FROM dbo.YourTable t2
WHERE c.Code = t2.Code
AND DATEDIFF(day, t2.[Date], c.[Date]) BETWEEN 0 AND 1
) o
WHERE c.Code = o.Code AND c.[Date] = o.[Date]
ORDER BY c.[Date]
Demo su SQLFiddle
Per migliorare le prestazioni usa questo indice
CREATE INDEX x ON dbo.YourTable([Date], Code)
