si está utilizando SQL Server,
dateadd(DAY,0, datediff(day,0, created)) devolverá el día creado
por ejemplo, si la venta se creó el '2009-11-02 06:12:55.000',dateadd(DAY,0, datediff(day,0, created)) volver '2009-11-02 00:00:00.000'
select sum(amount) as total, dateadd(DAY,0, datediff(day,0, created)) as created
from sales
group by dateadd(DAY,0, datediff(day,0, created))
