关于将SQL数据库查询结果写入txt文件的问题

Question

代码如下：
    adoquery1.close;
    adoquery1.sql.clear;
    adoqueyr1.sql.add('select sum(要素) as sum from table where 时间 between date1 and date2 and id=12);
    adoquery1.open;
    r:=adoquery1.fieldbyname('sum).asstring;    path:=extractfilepath(application.exename);
    assignfile(f,path+'test.txt');
    rewrite(f);
    writeln(f,r);
    closefile(f);报警信息： Illegal type in write/writeln statement;

Answer 1

在Write/Writeln语句中存在非法类型

Answer 2

procedure TForm1.btn1Click(Sender: TObject);
var
  F:textfile;
  r:string;
  path:string;
begin
  r:=adoquery1.fieldbyname('sum').asstring;
  path:=extractfilepath(application.exename)+'test.txt';
    AssignFile(F,path);
    if FileExists(path) then
    begin
    ReSet(F);
    Append(F);
    end
    else
    begin
    ReWrite(F);
    end;
   writeln(f,r);
   closefile(f);
end;