如何检查，如果数据库是空的，或者不通过C＃ComboBox的

if ((comboBox5.SelectedIndex==-1) || (comboBox6.SelectedIndex==-1) || (comboBox3.SelectedIndex==-1) || (comboBox7.SelectedIndex==-1))

            {

                MessageBox.Show("Data base has been empty");

               

            }