1. 當datatable 已存在於一個dataset中是，可以使用 ds.tables.add(dt.copy()) 來想dataset 中新增datatable;

2. 在查詢表格時，如果想查詢兩個欄位，只當兩個欄位都相同時才過濾重複保留唯一，否則不過濾，這是可以這樣使用distinct:

select  distinct  a, b  from  table1

3. 今天在往devexpress 中的treelist 控制元件中新增節點時，發現雖然新增上了但是介面不顯示節點值，解決辦法是在設計器裡先給treelist新增一個列（當然，我的需求是隻有一列的情況下），然後隱藏它即可。為什麼要新增一列呢？因為在後臺程式碼裡我們是這樣寫的：

TreeListNode FirstLevelNode = treeList1.AppendNode(null, root);
FirstLevelNode.SetValue(treeList1.Columns[0], drFirstLevelNode["StateName"].ToString().Trim());

這裡的  treeList1.Columns[0]  就是我們新增的那一行（我自己理解的，不知道對不對，反正實踐顯示不新增就沒法顯示）。

最後附上完整的往dev treelist 中根據資料庫中資料動態新增節點程式碼：

WellDAL dalWell = new
 
 WellDAL();
            TreeListNode root = treeList1.AppendNode(null, null);
            root.SetValue(treeList1.Columns[0], "本地資料庫");
            //第一層節點
            DataTable dtFirstLevelNode = new DataTable();
            dtFirstLevelNode = dalWell.GetData("StateName");
            foreach (DataRow drFirstLevelNode in
 
 dtFirstLevelNode.Rows)
            {
                TreeListNode FirstLevelNode = treeList1.AppendNode(null, root);
                FirstLevelNode.SetValue(treeList1.Columns[0], drFirstLevelNode["StateName"].ToString().Trim());
                //第二層節點
                DataTable dtSecondLevelNode = new DataTable();
                dtSecondLevelNode = dalWell.GetData("StateName", "FieldName");
                foreach (DataRow drSecondLevelNode in dtSecondLevelNode.Rows)
                {
                    if (drSecondLevelNode["StateName"].ToString().Trim() == drFirstLevelNode["StateName"].ToString().Trim())
                    {
                        TreeListNode SecondLevelNode = treeList1.AppendNode(null, FirstLevelNode);
                        SecondLevelNode.SetValue(treeList1.Columns[0], drSecondLevelNode["FieldName"].ToString().Trim());
                        //第三層節點
                        DataTable dtThirdLevelNode = new DataTable();
                        dtThirdLevelNode = dalWell.GetData("StateName", "FieldName", "BlockName");
                        foreach (DataRow drThirdLevelNode in dtThirdLevelNode.Rows)
                        {
                            if (drThirdLevelNode["StateName"].ToString().Trim() == drFirstLevelNode["StateName"].ToString().Trim() && drThirdLevelNode["FieldName"].ToString().Trim() == drSecondLevelNode["FieldName"].ToString().Trim())
                            {
                                TreeListNode ThirdLevelNode = treeList1.AppendNode(null, SecondLevelNode);
                                ThirdLevelNode.SetValue(treeList1.Columns[0], drThirdLevelNode["BlockName"].ToString().Trim());
                                //第四層節點
                                DataTable dtForthLevelNode = new DataTable();
                                dtForthLevelNode = dalWell.GetData("StateName", "FieldName", "BlockName", "WellName");
                                foreach (DataRow drForthLevelNode in dtForthLevelNode.Rows)
                                {
                                    if (drForthLevelNode["StateName"].ToString().Trim() == drFirstLevelNode["StateName"].ToString().Trim() && drForthLevelNode["FieldName"].ToString().Trim() == drSecondLevelNode["FieldName"].ToString().Trim() && drForthLevelNode["BlockName"].ToString().Trim() == drThirdLevelNode["BlockName"].ToString().Trim())
                                    {
                                        TreeListNode ForthLevelNode = treeList1.AppendNode(null, ThirdLevelNode);
                                        ForthLevelNode.SetValue(treeList1.Columns[0], drForthLevelNode["WellName"].ToString().Trim());
                                        //第五層節點
                                        DataTable dtFifthLevelNode = new DataTable();
                                        dtFifthLevelNode = dalWell.GetData("StateName", "FieldName", "BlockName", "WellName", "HoleNumber");
                                        foreach (DataRow drFifthLevelNode in dtFifthLevelNode.Rows)
                                        {
                                            if (drFifthLevelNode["StateName"].ToString().Trim() == drFirstLevelNode["StateName"].ToString().Trim() && drFifthLevelNode["FieldName"].ToString().Trim() == drSecondLevelNode["FieldName"].ToString().Trim() && drFifthLevelNode["BlockName"].ToString().Trim() == drThirdLevelNode["BlockName"].ToString().Trim() && drFifthLevelNode["WellName"].ToString().Trim() == drForthLevelNode["WellName"].ToString().Trim())
                                            {
                                                TreeListNode FifthLevelNode = treeList1.AppendNode(null, ForthLevelNode);
                                                FifthLevelNode.SetValue(treeList1.Columns[0], drFifthLevelNode["HoleNumber"].ToString().Trim());
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
            treeList1.ExpandAll();

 效果圖：