맞춤형 자판 번호를 얻는 방법은 무엇입니까?

Question

자 동 번호에서 사용자 지정 자동 번호를 얻으려고합니다. 그러나 데이터베이스 테이블에 데이터가 있으면 원활하게 실행되며 데이터베이스 테이블에 데이터가 없으면 오류가 발생합니다.

Private Sub CustomNo() 
    Dim comm As OleDbCommand 
    Dim commStr As String = "SELECT MAX(ID) FROM Table" 
    Dim RD As OleDbDataReader 
    Dim i As Integer 

    conn = New OleDbConnection(connStr) 
    conn.Open() 

    comm = New OleDbCommand(commStr, conn) 
    RD = comm.ExecuteReader 

    While RD.Read 
     If Not IsDBNull(RD.GetInt32(0)) = False Then 
      i = RD.GetInt32(0) 
      CustN = "ABC-" & i + 1 
      Custom_NoTextBox.Text = CustN 
      Exit While 
     Else 

      i = 0 
      CustN = "ABC-" & i + 1 
      Custom_NoTextBox.Text = CustN 

     End If 
    End While 

    conn.Close() 
End Sub 

Answer 1

Private Sub CustomNo() 

    Dim CountCom As OleDbCommand 
    Dim CountComStr As String = "SELECT COUNT(*) FROM Table" 
    Dim j As Integer 
    Dim i As Integer 

    conn = New OleDbConnection(connStr) 
    conn.Open() 

    CountCom = New OleDbCommand(CountComStr, conn) 
    j = CountCom.ExecuteScalar() 

    If j = 0 Then 
     i = 1 
    Else 
     Dim comm As OleDbCommand 
     Dim commStr As String = "SELECT MAX (ID) FROM Table" 
     Dim RD As OleDbDataReader 

     comm = New OleDbCommand(commStr, conn) 
     RD = comm.ExecuteReader 
     While RD.Read 
      i = RD.GetInt32(0) 
     End While 
     i = i + 1 
    End If 

    Custom_NoTextBox.Text = "ABC-" & i 

    conn.Close() 
End Sub