数据库的建立与链接问题

dim Objcn as new connection,objRs as new recordset
objcn.connectionstring="Prvider=Microsoft.jet.OLEDB.3.5.1;" & _
"data sourse=数据远文件路径" '连接数据提供者与数据源
objcn.open
 strSQL=“select ……from …… where……”
set objrs.activeconnection=objcn '将数据库记录集与数据源相匹配
objrs.open(strSQL) '记录集打开
 . ‘进行数据库的增删改查操作
objcn.close ‘关闭数据库
set objrs=Nothing
set objcn=Nothing

set objcn=new connection
objcn.open="dsn=数据库文件名"
set objrs=new recordset
 .
objcn.close
set objrs=nothing
set objcn=nothing

Private Declare Function GetUsername Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpBuffer As String, nSize As Long) As Long

Private Sub Form_Load()
 Dim sbuffer As String
 Dim lsize As Long
 
 sbuffer = Space$(255) '因无法确定系统用户名的长度，先开辟一个255（最大值）空格字符控件
 lsize = Len(sbuffer) 'lsize盛放sbuffer字符串的真是长度
 Call GetUsername(sbuffer, lsize) 
 'api中字符串作函数，需要提前确定大小
 
 If lsize > 0 Then
 txtusername.Text = Left$(sbuffer, lsize)
 Else
 txtusername.Text = vbNullString
 '没有字符串
 End If
 
 ok = False
 micount = 0 ’用于登陆次数的标记
 End Sub

Private Sub cmdOK_Click()
 Dim txtSQL As String
 Dim mrc As ADODB.Recordset '用于保存数据源记录集
 Dim MsgText As String
 
 UserName = "" '先将登录名滞空
 If Trim(txtusername.Text = "") Then '确认用户名输入框不为空
 MsgBox "没有这个用户，请重新输入用户", vbOKOnly + vbExclamation, "警告"
 txtusername.SetFocus
 Else
 txtSQL = "select * from user_info where user_id ='" & txtusername.Text & "'"
 Set mrc = ExecuteSQL(txtSQL, MsgText) '
 调用模块当中的executesql函数
建立数据库连接
 If mrc.EOF Then
 MsgBox "没有这个用
户，请重新输入用户", vbOKOnly + vbExclamation, "警告"
 txtusername.SetFocus
 Else '确认密码
 If Trim(mrc.Fields(1)) = Trim(txtpassword.Text) Then
 ok = True
 mrc.Close
 Me.Hide
 UserName = Trim(txtusername.Text)
 frmmain.Show
 Else
 MsgBox "输入密码不正确，请重新输入！", vbOKOnly + vbExclamation, "警告"
 txtpassword.SetFocus
 txtpassword.Text = ""
 End If
 End If
 End If
 
 micount = micount + 1 '值允许3次输入
 If micount = 3 Then
 Me.Hide
 End If
 Exit Sub
 
End Sub

Public Function ConnectString() As String
 ConnectString = "FileDSN=student.dsn;UID=sa;PWD=123" '文件源，登录名，验证密码
End Function
Public Function ExecuteSQL(ByVal SQL As String, MsgString As String) As ADODB.Recordset
 Dim cnn As ADODB.Connection
 Dim rst As ADODB.Recordset
 Dim sTokens() As String
 
 'On Error GoTo ExecuteSQL_Error
 
 sTokens = Split(SQL) '该函数定义将sql语句中的词以空格为分解符分解开放进一个数组里
 Set cnn = New ADODB.Connection '实体化，连接数据源
 cnn.Open ConnectString '打开数据源
 
 If InStr("INSERT,DELETE,UPDATE", UCase$(sTokens(0))) Then '比较确定sql数据开始单词是否为增，删，改
 cnn.Execute SQL '执行SQL语句
 MsgString = sTokens(0) & " query successful"
 '虽然MsgString不是返回值，但传递方式是ByRef，实参地址和这个地址相同
 Else
 Set rst = New ADODB.Recordset '实例化记录集
 rst.Open Trim$(SQL), cnn, adOpenKeyset, adLockOptimistic '打开要执行的内容sql，连接数据源，游标类型：键集游标,窗口值固定大小
 '得到临时表，游标指向第一条记录
 'get RecordCount，
 Set ExecuteSQL = rst
 MsgString = "查询到" & rst.RecordCount & _
 " 条记录 "
 End If
 
ExecuteSQL_Exit: ‘关闭连接
 Set rst = Nothing
 Set cnn = Nothing
 Exit Function
 
ExecuteSQL_Error:
 MsgString = "查询错误: " & _
 Err.Description
 Resume ExecuteSQL_Exit
End Function