# sql to calculate date differences in same column
# SELECT B.*
# FROM
# (SELECT ordernum, agent, MIN([datetime]) AS mindatetime
# FROM YourTable
# GROUP BY ordernum, agent) AS A
# JOIN YourTable AS B
# ON A.ordernum = B.ordernum
# AND A.agent = B.agent
# AND (A.mindatetime = B.[datetime] OR DATEADD(minute, 120, A.mindatetime) <= B.[datetime])