probeer onderstaande zoekopdracht
select CONVERT(decimal(18,2),SUM(Effort1 + Effort2)) +
SUM(Effort1Minutes + Effort2Minutes) / 60 +
CONVERT(decimal(18,2), (SUM(Effort1Minutes + Effort2Minutes) % 60) / 100.00)
from TimesheetDetails
Ik had met deze query getest met SQL server 2008 en met SQL Fiddle