Automatically Update Values in Database from DataGridView

I'm currently working on a project using MySql in combination with C#. The Data for the DataGridView is provided by a join from multiple tables in the DB. To show the data I use the following, working, code:

adapter.SelectCommand = new MySqlCommand(
            " SELECT" +
            " l.lot AS Lot, "+
            " m.comment AS Bemerkungen," +
            ... (multiple columns from different tables) ...
            " FROM m " +
            " JOIN m2p ON m.m2p_id = m2p.id" +
            ... (more joins) ...
            , this._mySqlConnection);
dataGridView1.DataSource = data;
adapter.Fill(data);

Now the user of the GUI is allowed to modify a certain column (the "comment" column). So I assigned an eventHandler to the CellEndEdit event and when the user modified the allowed column the adapter.Update(data) is called. Now this doesn't perform the correct action.

To define my updatecommand I used the following code:

adapter.UpdateCommand = new MySqlCommand(
                " UPDATE m" +
                " JOIN  l ON m.l_id = l.id" +
                " SET m.comment = @comment" +
                " WHERE l.lot = @lot"
                , this._mySqlConnection);
adapter.UpdateCommand.Parameters.Add("@comment", MySqlDbType.Text, 256, "Bemerkungen");
adapter.UpdateCommand.Parameters.Add("@lot", MySqlDbType.Text, 256, "Lot");

Could you explain me how I fix my code to automatically Update the database?

EDIT: added further source code:

private MySqlDataAdapter warenlagerMySqlDataAdapter, kundenMySqlDataAdapter;
private DataTable warenlagerData, kundenData;
private DataGridView warenlagerGridView;

private void updateWarenlagerView(object sender, EventArgs e) {
            warenlagerMySqlDataAdapter.Update(warenlagerData);
}

private void initialzeFields() {
            warenlagerGridView.CellEndEdit += new DataGridViewCellEventHandler(this.updateWarenlag