How can I group by date time column without taking time into consideration

In pre Sql 2008 By taking out the date part:

GROUP BY CONVERT(CHAR(8),DateTimeColumn,10)

GROUP BY DATEADD(day, DATEDIFF(day, 0, MyDateTimeColumn), 0)

Or in SQL Server 2008 onwards you could simply cast to Date as @Oded suggested:

GROUP BY CAST(orderDate AS DATE)

Cast/Convert the values to a Date type for your group by.

GROUP BY CAST(myDateTime AS DATE)

CAST datetime field to date

select  CAST(datetime_field as DATE), count(*) as count from table group by CAST(datetime_field as DATE);