為什麼OLEDBDATAADAPTER不能更新數據!

[XJFJX15]

我的程序代碼是這樣的
Sub load_data(ByVal sa_list As String)
con.ConnectionString = con_db()
con.Open()
If sa_list = "" Then
dataadapter = New OleDbDataAdapter("select * from sa_list", con)
Else
dataadapter = New OleDbDataAdapter("select * from sa_list='" & Trim(sa_list) & "'", con)
End If

dataadapter.Fill(mydataset)
con.Close()


End Sub

sub add()
Dim mydatarow As DataRow
mydatarow = mydataset.Tables(0).NewRow()
mydatarow.BeginEdit()
mydatarow.Item("sa_list") = "A612"
mydatarow.Item("sa_no") = "sdfsdf"
mydatarow.Item("sa_date") = "2006/02/05"
mydatarow.EndEdit()
mydataset.Tables(0).Rows.Add(mydatarow)
Dim mycmd As OleDbCommandBuilder = New OleDbCommandBuilder(dataadapter)
dataadapter.Update(mydataset)
DataGridView1.DataSource = mydataset.Tables(0)
end
這樣在mydataset是增加了數據，為什麼dataadapter update後寫不到數據庫裡面。
我用的是access ,表名sa_list(sa_list text,sa_date text,sa_date text,uid 自動增長 主鍵)這樣的

急，這是什麼原因。