Vb.net 如果行存在，则要读取的查询

我需要知道行何时以及是否存在，我想使用ExecuteReader，对吗

我的代码只是想告诉你我要去哪里

Const c_str_SELECT_SQL As String = "SELECT Fails FROM LoginAttacks WHERE IP = ?"

If Not String.IsNullOrEmpty(strPointsDBConnectionString) Then
    objOLEConnection = New OleDbConnection(strPointsDBConnectionString)
    objOLEConnection.Open()
    objOLECommand = New OleDbCommand(c_str_SELECT_SQL, objOLEConnection)
    objIP = objOLECommand.Parameters.Add("@IP", OleDbType.Char)
    objIP.Value = Me.IPAddress

    ' Connect execute update query
    FailedCounts = CInt(objOLECommand.ExecuteScalar())

    If FailedCounts > 0 Then 'need to find way to tell if query worked/found row with ip
        FailedCounts = FailedCounts + 1
        'Did not fail assume worked so go use update function
        IPExist = True 'if not go use insert function
    End If
Else
    Throw New Exception(const_CONNECTION_STRING_ERROR)
End If

更新：

我补充说：

objOLEDataReader = objOLECommand.ExecuteReader()

If objOLEDataReader.HasRows Then
    'Do While objOLEDataReader.Read()
    FailedCounts = CInt(objOLECommand.ExecuteScalar())
    FailedCounts = FailedCounts + 1
    'Did not fail assume worked so go use update function
    IPExist = True 'if not go use insert function
    'Loop
Else
    'none found
End If

objOLEDataReader.Close()

但是，即使有行，我似乎也不会使用IF语句。

如果没有数据，

ExecuteScalar

将返回

Nothing

。因此，您应该首先能够检查

Nothing

，以了解是否有行：

Dim FailedCountsObject As Object = objOLECommand.ExecuteScalar()

'need to find way to tell if query worked/found row with ip
If FailedCountsObject IsNot Nothing Then
    FailedCounts = CInt(FailedCountsObject)
    FailedCounts = FailedCounts + 1
    'Did not fail assume worked so go use update function
    IPExist = True 'if not go use insert function
End If