Vb.net 他接受了答案。。。 con = New OleDbConnection(cs) con.Open() Dim ct As String = "SELECT RoomNo FROM Temp_Reservation WHERE RoomNo='" _ &

他接受了答案。。。

con = New OleDbConnection(cs)
con.Open()
Dim ct As String = "SELECT RoomNo FROM Temp_Reservation WHERE RoomNo='" _
  & cmbRoomNo.Text & "' AND DateOut BETWEEN  #" & dtpDateIN.Text _
  & "# AND  #" & dtpDateOut.Text _
  & "# AND Status='Confirmed' AND DateIN < #" & dtpDateOut.Text & "#"
cmd = New OleDbCommand(ct)
cmd.Connection = con
rdr = cmd.ExecuteReader()
If rdr.Read Then
    MessageBox.Show("Selected Room is already booked", "Input Error", _
                    MessageBoxButtons.OK, MessageBoxIcon.Error)
    If Not rdr Is Nothing Then
        rdr.Close()
    End If
    Exit Sub
End If

Temp_Reservation.DateIn < new_out AND Temp_Reservation.DateOut > new_in
    ==> booking conflict!

 Reservation A:   26/12/2013 to 28/12/2013  
 Reservation B:   10/01/2014 to 15/01/2014  
 Reservation new: 01/01/2014 to 05/01/2014  

 A_in(26/12/2013) < new_out(05/01/2014) AND A_out(28/12/2013) > new_in(01/01/2014)
     ===> True AND False = False (which means: no conflicting record will be returned)

  B_in(10/01/2014) < new_out(05/01/2014) AND B_out(15/01/2014) > new_in(01/01/2014)
     ===> False AND True = False

OK:        A_in >= B_out OR A_out <= B_in

CONFLICT:  A_in < B_out AND A_out > B_in

Dim ct As String
ct = String.Format("Select RoomNo from Temp_Reservation where RoomNo=""{0}""" & _
                   "And Status = ""Confirmed"" And " & _
                   "(#{1}# < DateOut And #{1}# >= DateIn) " & _
                   "Or (#{2}# > DateIn  And #{2}# <= DateOut) " & _
                   "Or (#{1}# < DateIn And #{2}# > DateOut)", _
                   cmbRoomNo.Text, dtpDateIN.Text, dtpDateOut.Text)