It's best to check each field separately. Also you need to exit the sub. So instead of
If txtFNAppointment.Text & txtMNAppointment.Text & txtLNAppointment.Text ="" Then
MessageBox.Show("Please fill-up all the required fields !")
try
If txtFNAppointment.Text = "" Or txtMNAppointment.Text = "" Or txtLNAppointment.Text ="" Then
MessageBox.Show("Please fill-up all the required fields !")
Return
End If
And what comes to your query, never concatenate values directly into the SQL statement. This leaves you open to SQL injections. Instead, use
SqlParameter[
^]. For more discussion, see
Properly executing database operations, version 3, parameters[
^]