How To Makes Sum In Sql

I want to get different sums from an item base. I have taken the number of every order (ord) from an order base and goes to the item-base like this:

Set Rss = Server.CreateObject("ADODB.RecordSet")
sSQL= "SELECT array(sum(numitems)) from oitems where orderid= " & ord
Rss.Open sSQL, sDSN, adOpenStatic, adLockReadOnly, adCmdText

I have not tried to run the sql- the array is just a dummy to show the idea.

Actually I want to make an array of the sum of items with the same numitems (i.e. the same productnumber)

if the sql runs I will write the array like this:

While Not rss.eof
response.write array(sum(numitems))
'or whatever way I have to write it
rss.Movenext
Wend

...anyone who has a good idea of how to do this?