下面是我的代码，但好象没有效果，不知是怎么回事，请那位高手帮看一下，指点一二。
Dim ZDM As String
Try
'construct the command object and open a connection to the Contacts table

Dim cmdString As String = "Select ZDM from DZB WHERE ZMC = " & Grid1.Cell(j, 4).Text & " "
Dim connString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=hjsby.mdb"
Dim myConnection As OleDbConnection = New OleDbConnection(connString)

' Open connection
myConnection.Open()

'Create OleDbCommand object
Dim TheCommand As OleDbCommand = New OleDbCommand(cmdString, myConnection)

TheCommand.CommandType = CommandType.Text
' Create a DataReader and call Execute on the Command Object to construct it

Dim TheDataReader As OleDbDataReader = TheCommand.ExecuteReader()

While TheDataReader.Read()

ZDM = TheDataReader("ZDM").ToString()

End While
Catch ae As OleDbException
MsgBox(ae.Message())
End Try