What you want to do here is persist the data you are loading to QVD, using the STORE statement.
If you have a unique ID in sql.table you can then use WHERE EXISTS to only load rows from the persisted QVD which are not in the latest load. Something like this:
// Get recent rows
table:
LOAD * FROM sql.table WHERE date >= today()-3;
// If QVD present add from here
if alt(FileSize('lib://DataFiles/MyQVD.qvd'), 0) > 0 then
CONCATENATE(table)
LOAD * FROM [lib://DataFiles/MyQVD.qvd] (qvd)
WHERE NOT EXISTS (ID);
end if
// Write all data back to QVD
STORE table INTO [lib://DataFiles/MyQVD.qvd] (qvd);
The store and load to a QVD is very quick and doing it this way means the data is persisted and can be shared between different applications. The partial load functionality in Sense is not used.
If there is no unique ID on the table then you need to think a bit more about how the incremental load will work. Trying to get to the point where a WHERE EXISTS can be used is important, as this allows an optmised QVD load.
If you have a transactional table you don't even need to go back three days, you could get the time of the last load and simply load since that time (perhaps with a little added to account for daylight saving once a year and a bit of a buffer).
