private void PUButton_Click_17(object sender, RoutedEventArgs e)
        {
            int    i = SQLTextBox.SelectionStart;
            string s = SQLTextBox.Text;

            s = s.Insert(i, " NULL ");
            SQLTextBox.Text = s;
            SQLTextBox.Focus();
            SQLTextBox.Select(i + 6, 0);
        }
        /// <summary>
        /// 选择字段名
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void AttrListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (AttrListView.SelectedIndex == -1)
            {
                return;
            }
            int    i    = SQLTextBox.SelectionStart;
            string s    = SQLTextBox.Text;
            string name = FldsNames[AttrListView.SelectedIndex];

            s = s.Insert(i, name);
            SQLTextBox.Text            = s;
            AttrListView.SelectedIndex = -1;
            SQLTextBox.Focus();
            SQLTextBox.Select(i + name.Length, 0);
        }
        /// <summary>
        /// 使用函数
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void PUComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            int    i = 0;
            string s = "";

            switch (FuncComboBox.SelectedIndex)
            {
            case -1:
                break;

            case 0:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " abs() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 5, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 1:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Max() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 5, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 2:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Min() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 5, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 3:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Round() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 7, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 4:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Lower() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 7, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 5:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Upper() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 7, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            case 6:
                i = SQLTextBox.SelectionStart;
                s = SQLTextBox.Text;
                s = s.Insert(i, " Substr() ");
                SQLTextBox.Text = s;
                SQLTextBox.Focus();
                SQLTextBox.Select(i + 8, 0);
                FuncComboBox.SelectedIndex = -1;
                break;

            default:
                break;
            }
        }