如何实现日期的比较？

放两个DateTimePicker控件进行比较就行了,我以前做过类似的，给点代码你参考下。。
if CheckBoxtime.Checked=true   then
   begin
     if DateTimePicker1.DateTime>DateTimePicker2.DateTime then
       begin showmessage('查询时间有误，请正确选择查询时间!');exit;end;
   end;
 if CheckBoxtime.Checked=true   then
   begin
     if DateTimePicker1.DateTime<DateTimePicker2.DateTime then
      begin
      wherestr:=wherestr+' ( ReTime>='''+datetimetostr(DateTimePicker1.DateTime)+''' and ReTime<='''+datetimetostr(DateTimePicker2.DateTime)+''')';
      wherestr1:='and';
      end;
   end;