如何使用vb.net在mysql数据库中查找每台机器id的最后一行？

像这样的东西应该有用

    Private Sub btnAddSchedule_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddSchedule.Click
    Try
        Dim ts As TimeSpan = TimeSpan.Parse(Me.dtpSchedule.Text

        ' PROBLEM IN HERE ??? 
        Dim rwFound As DataRow = MyDataset.Tables("totalizer_setting").Rows.Find( ??? )
        If IsNothing(rwFound) Then
        Dim rw As DataRow = MyDataset.Tables("totalizer_setting").NewRow
        rw("machine_id") = Me.txtMachineID.Text
        rw("time_schedule") = ts
        rw("product_quantity") = DBNull.Value
        MyDataset.Tables("totalizer_setting").Rows.Add(rw)

        Dim sql As String = String.Format("INSERT INTO {0}.totalizer_setting (machine_id, time_schedule, product_quantity) VALUES ({1});", varSchema, "@machine_id, @time_schedule, @product_quantity")
        Dim cmd As New MySqlCommand(sql, objCon)
        cmd.Parameters.AddWithValue("@machine_id", Me.txtMachineID.Text)
        cmd.Parameters.AddWithValue("@time_schedule", ts)
        cmd.Parameters.AddWithValue("@product_quantity", DBNull.Value)
        MyDataAdapter.InsertCommand = cmd
        MyDataAdapter.Update(MyDataset, "totalizer_setting")
        cmd.Dispose()

       End If
    Catch ex As MySqlException
        MessageBox.Show("Error occurred in btnAddSchedule_Click Function" & vbCrLf & ex.Number & " – " & ex.Message)
    End Try
End Sub

再想一想，我不知道mysql是否有

last（）

函数（sql server有）。如果mysql没有，您可以按相反顺序使用

first（）

，或者查看中的答案，以获得更有效的解决方案

    Private Sub btnAddSchedule_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddSchedule.Click
    Try
        Dim ts As TimeSpan = TimeSpan.Parse(Me.dtpSchedule.Text

        ' PROBLEM IN HERE ??? 
        Dim rwFound As DataRow = MyDataset.Tables("totalizer_setting").Rows.Find( ??? )
        If IsNothing(rwFound) Then
        Dim rw As DataRow = MyDataset.Tables("totalizer_setting").NewRow
        rw("machine_id") = Me.txtMachineID.Text
        rw("time_schedule") = ts
        rw("product_quantity") = DBNull.Value
        MyDataset.Tables("totalizer_setting").Rows.Add(rw)

        Dim sql As String = String.Format("INSERT INTO {0}.totalizer_setting (machine_id, time_schedule, product_quantity) VALUES ({1});", varSchema, "@machine_id, @time_schedule, @product_quantity")
        Dim cmd As New MySqlCommand(sql, objCon)
        cmd.Parameters.AddWithValue("@machine_id", Me.txtMachineID.Text)
        cmd.Parameters.AddWithValue("@time_schedule", ts)
        cmd.Parameters.AddWithValue("@product_quantity", DBNull.Value)
        MyDataAdapter.InsertCommand = cmd
        MyDataAdapter.Update(MyDataset, "totalizer_setting")
        cmd.Dispose()

       End If
    Catch ex As MySqlException
        MessageBox.Show("Error occurred in btnAddSchedule_Click Function" & vbCrLf & ex.Number & " – " & ex.Message)
    End Try
End Sub

select last(time_schedule), last(product_quality) from yourTable group by machine_id