QSqlRelationalTableModel should return records even if it cannot find the relations for it in the second/third.. tables

Currently we use WHERE condition in QSqlRelationalTableModel to filter the records without relations. However this doesn't conform to the general idea.
The records of the main table should always be returned even if there is not relation found. The main fields should be filled in, and relational fields should be empty in this case.

This problem can be reproduced using examples/sql/relationaltablemodel/. Change relationaltablemodel.cpp, around line 90:
query.exec("insert into city values(100, 'San Jose')"); //change 100 to 101

Because internally Qt uses the following sql command to query the data:
"SELECT employee."id", employee."name", relTblAl_2.name
AS city_name_3, relTblAl_3.name AS country_name_2
FROM employee, city relTblAl_2, country relTblAl_3
WHERE (employee."city" = relTblAl_2.id AND employee."country" = relTblAl_3.id) "

The WHERE condition causes the records without relations are not returned to the view.