dbchart不能显示同个字段的不同数据 ( 积分: 100 )

我的代码如下:
try
with DM.ADOQuery1do
begin
DBChart1.Title.Text.Clear;
dm.ADOQuery1.Close;
dm.ADOQuery1.SQL.Clear;
dm.ADOQuery1.SQL.Add('select s_kind,sum(s_num) as 总数1 from space '+'where u_name=:u_name group by s_kind');

dm.ADOQuery1.Parameters.ParamByName('u_name').Value :=u_name_cb.Text;
dm.ADOQuery1.Open;
dm.ADOQuery1.ExecSQL;
if ComboBox1.Text='饼图' then
begin
DBChart1.Title.Text.Add(u_name_cb.text);
DBChart1.Series[0].Active:=true;
DBChart1.Series[1].Active:=false;
DBChart1.Series[0].DataSource:=dm.ADOQuery1;
DBChart1.Series[0].XLabelsSource:='s_kind';
DBChart1.Series[0].YValues.ValueSource:='总数1';
end
else
if ComboBox1.Text='柱型图' then
begin
DBChart1.Title.Text.Add(u_name_cb.text);
DBChart1.Series[0].Active:=false;
DBChart1.Series[1].Active:=true;
DBChart1.Series[1].DataSource:=dm.ADOQuery1;
DBChart1.Series[1].XLabelsSource:='s_kind';
DBChart1.Series[1].YValues.ValueSource:='总数1';
end;
end;
except
MessageDlg('【'+u_name_cb.Text+'】显示失败',mtError,[mbok],0);
Exit;
end;

功能:
表space(u_name,s_kind,s_num)字段有多个数据,根据u_name的不同,用饼图(或者柱型图可以选择)显示s_kind和sum(s_num)字段的不同数据.
问题:
现在是当u_name:=dinghai1时(饼图)显示正常,但当u_name:=dinghai2时却不能刷新,只能显示当u_name:=dinghai1时的数据,但DBChart1.Title刷新正常.但当ComboBox1.Text发生变化时(柱型图)却又能显示u_name:=dinghai2时数据.
请求各位高手解决.