Question about method named rowCount() of QSqlTableModel

[silentyears]

Hi all,
After i use QSqlTableModel to get one table in database, i want to handle every row in table ,so i code as follows:

QSqlTableModel  tableModel;
tableModel->setTable(tableA);
tableModel->select();
int nCount = tableModel->rowCount();
for(int i=0, i<nCount, i++)
{
   // handle every row
   //  ....
}

QSqlTableModel  tableModel;
tableModel->setTable(tableA);
tableModel->select();
int nCount = tableModel->rowCount();
for(int i=0, i<nCount, i++)
{
   // handle every row
   //  ....
}

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here is my question, why the value of nCount is less than the real rows' count(Observed from database table view)? And the value is 256, could i get whole rows when the count of rows are so many like tens of thousands? Or is there any smarter idea to do the same work?
Thank you!