Incremental loads can be done in multiple ways depending on how data is updated and the needs of the business.
Here is a simple approach fetching all new rows based on the Day field.
I assume you have an inc_data.qvd with previous loaded data.
inc_data:
Load *
From inc_data.qvd (qvd);
TmpMaxDay:
LOAD Max(Day) as MaxDay;
LOAD FieldValue('Day', recno()) as Day
AUTOGENERATE FieldValueCount('Day');
Let vMaxDay = peek('MaxDay',-1,'TmpMaxDay')
Concatenate (inc_data)
Load * from DataSource
Where Day > $(vMaxDay);
Store inc_data into inc_data.qvd (qvd);