请大家帮忙看看是什么错误,谢谢了!

Question

当程序运行时,出现"mismatch in express"我感觉好像是sql那有错误.请大家给我指正一下.谢谢了.
procedure TForm1.ComboBox2Change(Sender: TObject);
var
gradepartment :string;
sql:string;
iteminde:integer;
begin
  iteminde:=combobox2.ItemIndex+1;
  if(iteminde<=9) then
      begin
     gradepartment:=combobox1.Text+'0'+inttostr(iteminde);
      end
  else
      begin
      gradepartment:=combobox1.Text+inttostr(iteminde);
      end;
 sql:='select * from classdata where grade='+gradepartment;
 query1.Close;
 query1.SQL.Clear;
 query1.SQL.Add(sql);
 query1.ExecSQL;
 query1.Open;
 query1.UnPrepare;
end;end.

Answer 1

试试sql:='select * from classdata where grade='''+gradepartment+'''';

Answer 2

mismatch in express
表达式不匹配，少了单引号