In QV Reference Manual, page 401 (v11 SR2), there is a sample code for Insert And Update incremental load:
SQL SELECT PrimaryKey, X, Y
WHERE ModificationTime >= #$(LastExecTime)#;
LOAD PrimaryKey, X, Y
WHERE NOT Exists(PrimaryKey);
STORE QV_Table INTO File.QVD;
* The key here is to first load from the DB all the Inserted/Updated records since the last reload. Then, you concatenate the data from the QVD file, using the exists() function to only concatenate the records which PrimaryKey don't match.