Glycosuria. Means presence of sugar in the urine after a diet rich in abnormal amount of glucose or starches, and only then. Normally there is never sugar in urine. In diabetes, if blood sugars are high (>then 190mg%) the urine will have sugar present. So, an overwhelming amount of sugar that the Insulin could not push into the cells will be presented to the kidney and some will be spilled in the urine.
Alimentary glycosuri. This term refers to sugar appearing in the urine from abnormal amounts of sugar ingested into the system via the gastro-intestinal tract.