>The following SQL allows me to group by RO_No and collect a date time field with it:
>
>

>SELECT Event.RO_No,max(Event.DateTime) as LastDateTime FROM Event GROUP BY Event.RO_No
>

>
>However, I need to adjust that so the group by will only applies to the first 10 records of an order to Event.DateTime. Basically, if I wouldn't have a group by, the SQL would be this:
>
>

>SELECT TOP 10 Event.RO_No,Event.DateTime FROM Event ORDER by Event.DateTime
>

>
>But, on that result, I need to only get the unique occurence of Event.RO_No.

Are you working with SQL Server?

If yes, then

;with cte as (select top (10) Event.Ro_No, Event.[DateTime] from Event ORDER BY Event.DateTime)

select max(Event.DateTime) as LastDate, Event.Ro_No from cte