'數據源信息常量 Public Const conn As String = "Provider = SQLOLEDB.1;Password = sa; UserID = sa; Initial Catalog = StudentFiles; Data Source = localhost" Public Const CONNECT_LOOP_MAX = 10 '一次執行connect操作，可以訪問數據庫的次數 Private IsConnect As Boolean '標記數據庫是否連接 Private Connect_Num As Integer '標記執行Connect()函數后訪問數據的次數 Private cnn As ADDODB.Connection '連接數據庫的Connect對象  Private re As ADDODB.Recordset '保存結果集的Recordset對象//連接數據庫 Private Sub Connect() '如果連接標記為真，則返回。 IF IsConnect = True Then    Exit Sub End If Set cnn = New ADODB.Connection '關鍵new用于創建新對象cnn  cnn.ConnectionString = conn  cnn.Open '判斷連接的狀態 If cnn.State <> adStateOpen Then   MsgBox"數據庫連接失敗"   End End If '設置連接標識，表示已經連接到數據庫 IsConnect = TrueEnd Sub'斷開與數據庫的連接Private Sub DisConnect() Dim rc As Long If IsConnect = False Then   Exit Sub End If '關閉連接 cnn.Close '釋放cnn Set cnn = Nothing IsConnect = FalseEnd Sub'使用Connect_Num控制數據連接Public Sub DB_Connect()  Connect_Num = Connect_Num + 1  ConnectEnd Sub'使用Connect_Num控制數據斷開Public Sub DB_Disconnect()If Connect_Num >= CONNECT_LOOP_MAX Then  Connect_Num = 0  Disconnect End If End Sub'強制關閉api方式訪問俄的數據庫，計數器復位Public Sub DBapi_Disconnect()  Connect_Num = 0  DisconnectEnd Sub'執行數據庫操作語言'byval 就是按參數的值傳遞，再傳遞過程中，參數不會發生變化(也就是將參數值而不是將地址傳遞給過程的方式，這就使過程訪問發哦變量的副本，過程不可改變變量的值)；與之對應的是byref,指按參數的地址傳值，byref可以省略Public Sub SQLExt(ByVal TmpSQLstmt As String )    Dim cmd As New ADODB.Command '創建Command對象cmd    DB_Connect '連接數據庫    Set cmd.ActiveConnection = cnn '設置cmd的ActiveConnect屬性，指定與其關聯的數據庫連接  cmd.CommandText = TmpSQLstmt '設置要執行的命令文本  'MsgBox TmpSQLstmt  cmd.Execute '執行命令  Set cmd = Nothing  DB_DisConnect '斷開與數據庫的連接End Sub'執行數據庫查詢語句Public Function QueryExt(ByVal TmpSQLstmt As String ) As ADODB.Recordset    Dim rst As New ADODB.Recordset '創建Rescordset對象rst  DB_Connect '連接數據庫  Set rst.ActiveConnection = cnn '設置rst的ActiveConnection屬性,指定與其相關的數據庫的連接  rst.CursorType = adOpenDynamic '設置游標類型  rst.LockType = adLockOptimistic '設置鎖定類型  rst.Open TmpSQLstmt '打開記錄集  Set QueryExt = rst '返回記錄集  End Function