I have 3 fields, p_ID, unit_type, and Units

Unit_Type has 2 different values, 'sf' and 'u'

If 'u', then the Units field is fine but if 'sf', then i would like it to count the amount of times that p_id appears.

in access we used a Sum(IIF(unit_type='sf',1,Units)) AS Total_Units

I am having trouble doing this in SQL, any thoughts?