'數(shù)據(jù)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(zhí)行connect操作，可以訪問數(shù)據(jù)庫的次數(shù)

 Private IsConnect As Boolean '標(biāo)記數(shù)據(jù)庫是否連接

 Private Connect_Num As Integer '標(biāo)記執(zhí)行Connect()函數(shù)后訪問數(shù)據(jù)的次數(shù)

 Private cnn As ADDODB.Connection '連接數(shù)據(jù)庫的Connect對象
 
 Private re As ADDODB.Recordset '保存結(jié)果集的Recordset對象

//連接數(shù)據(jù)庫
 Private Sub Connect()
 '如果連接標(biāo)記為真，則返回。
 IF IsConnect = True Then 
   Exit Sub
 End If

 Set cnn = New ADODB.Connection '關(guān)鍵new用于創(chuàng)建新對象cnn
 
 cnn.ConnectionString = conn
 
 cnn.Open
 '判斷連接的狀態(tài)
 If cnn.State <> adStateOpen Then
   MsgBox"數(shù)據(jù)庫連接失敗"
   End
 End If

 '設(shè)置連接標(biāo)識，表示已經(jīng)連接到數(shù)據(jù)庫
 IsConnect = True
End Sub


'斷開與數(shù)據(jù)庫的連接
Private Sub DisConnect()
 Dim rc As Long

 If IsConnect = False Then
   Exit Sub
 End If
 '關(guān)閉連接
 cnn.Close
 '釋放cnn
 Set cnn = Nothing
 IsConnect = False
End Sub

'使用Connect_Num控制數(shù)據(jù)連接
Public Sub DB_Connect()
  Connect_Num = Connect_Num + 1
  Connect
End Sub

'使用Connect_Num控制數(shù)據(jù)斷開
Public Sub DB_Disconnect()
If Connect_Num >= CONNECT_LOOP_MAX Then
  Connect_Num = 0
  Disconnect
 End If
 End Sub

'強(qiáng)制關(guān)閉api方式訪問俄的數(shù)據(jù)庫，計數(shù)器復(fù)位
Public Sub DBapi_Disconnect()
  Connect_Num = 0
  Disconnect
End Sub

'執(zhí)行數(shù)據(jù)庫操作語言
'byval 就是按參數(shù)的值傳遞，再傳遞過程中，參數(shù)不會發(fā)生變化(也就是將參數(shù)值而不是將地址傳遞給過程的方式，這就使過程訪問發(fā)哦變量的副本，過程不可改變變量的值)；
與之對應(yīng)的是byref,指按參數(shù)的地址傳值，byref可以省略
Public Sub SQLExt(ByVal TmpSQLstmt As String )  

  Dim cmd As New ADODB.Command '創(chuàng)建Command對象cmd
  
  DB_Connect '連接數(shù)據(jù)庫
  
  Set cmd.ActiveConnection = cnn '設(shè)置cmd的ActiveConnect屬性，指定與其關(guān)聯(lián)的數(shù)據(jù)庫連接

  cmd.CommandText = TmpSQLstmt '設(shè)置要執(zhí)行的命令文本

  'MsgBox TmpSQLstmt

  cmd.Execute '執(zhí)行命令

  Set cmd = Nothing

  DB_DisConnect '斷開與數(shù)據(jù)庫的連接

End Sub

'執(zhí)行數(shù)據(jù)庫查詢語句
Public Function QueryExt(ByVal TmpSQLstmt As String ) As ADODB.Recordset
  
  Dim rst As New ADODB.Recordset '創(chuàng)建Rescordset對象rst

  DB_Connect '連接數(shù)據(jù)庫

  Set rst.ActiveConnection = cnn '設(shè)置rst的ActiveConnection屬性,指定與其相關(guān)的數(shù)據(jù)庫的連接

  rst.CursorType = adOpenDynamic '設(shè)置游標(biāo)類型

  rst.LockType = adLockOptimistic '設(shè)置鎖定類型

  rst.Open TmpSQLstmt '打開記錄集

  Set QueryExt = rst '返回記錄集

  End Function