I have a select like this:

DECLARE @Success Bit

SET @Success=1

SELECT CONVERT(CHAR(4),YEAR(Invoice.ModDate)) AS lcChampNumero,COUNT(*) AS Compte,MIN(Invoice.ModDate) AS AddDate
 FROM Invoice (NOLOCK)
 INNER JOIN InvoiceStatus ON Invoice.NoInvoiceStatus=InvoiceStatus.Numero
 INNER JOIN Client ON Invoice.NoClient=Client.Numero
 WHERE (Invoice.Success=@Success) AND Invoice.NoSomething=2
 GROUP BY CONVERT(CHAR(4),YEAR(Invoice.ModDate))
 ORDER BY 1 DESC

I am looking at an alternative to boost up performance here. In some occasions, this can be very long. There are indexes on every fields. However, this GROUP BY thing on a big table may take up to 10 to 50 seconds sometimes.