游标返回null

Question

我有以下方法。

当我运行它时，列“D”返回空值但是如果我在sqllite管理器中运行打印的sql字符串，则有些值虽然有些行为空。

这是方法。

public List<ActiveTenancy> getUnInvoicedRooms(String mydate)
{
    List<ActiveTenancy> payments= new ArrayList<ActiveTenancy>();

        String sql ="SELECT Apartments.Number as N,Tenants.FirstName as F,Tenants.SurName as S ,"+
                   " (select Max(Rental_invoices.enddate)  from Rental_invoices inner Join Tenancy on Tenancy._id=Rental_invoices.tenancy_id "+
                  " where Tenancy.tenant_id=Tenants._id ) as D" +
                  " from Tenants "+               
                  " inner join Tenancy on Tenancy.tenant_id=Tenants._id "+
                 " inner join Apartments on Apartments._id=Tenancy.apartment_id "+
                " where Tenancy._id not  in(select  Rental_invoices.tenancy_id from Rental_invoices where enddate " + ">=?" + ")"+
                " and Tenancy.InActive=0";
 String[] args= new String[]{mydate};
        Log.e("sql", sql);
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c = db.rawQuery(sql, args);
        if(c.moveToFirst()){
            do{
                ActiveTenancy a= new ActiveTenancy();
                a.setFirstName(c.getString(c.getColumnIndex("F")));
                a.setSurname(c.getString(c.getColumnIndex("S")));
                a.setApartment(c.getString(c.getColumnIndex("N")));

                if(c.getString(c.getColumnIndex("D"))!=null)
                {
                    Log.e("dddd",c.getString(c.getColumnIndex("D")));
                try {
                    a.setEnd_date(fm.parse(c.getString(c.getColumnIndex("D"))));
                } catch (ParseException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                }
                payments .add(a);
            } while(c.moveToNext());
            }
         c.close();
    return payments;

}

造成这种情况的原因是什么？

罗纳德

不使用参数持有人“？”即将参数直接传递给sql语句，它现在正在工作。

String sql ="SELECT Apartments.Number as N,Tenants.FirstName as F,Tenants.SurName as S ,"+
                   " (select Max(Rental_invoices.enddate)  from Rental_invoices inner Join Tenancy on Tenancy._id=Rental_invoices.tenancy_id "+
                  " where Tenancy.tenant_id=Tenants._id ) as D" +
                  " from Tenants "+               
                  " inner join Tenancy on Tenancy.tenant_id=Tenants._id "+
                 " inner join Apartments on Apartments._id=Tenancy.apartment_id "+
                " where Tenancy._id not  in(select  Rental_invoices.tenancy_id from Rental_invoices where enddate " + ">='" + mydate + "'"+
                 ")"+
                " and Tenancy.InActive=0"; 

任何解释？....