表中有20个字段，字段名字就是1,2,3....20,写SQL语句时报错....

提示：标准表达式中类型不匹配！！为何呢？
for i:=1 to 20 do begin
   a[i]:=adoquery3.fieldbyname(inttostr(i+1)).asstring;
   if ssql='' then begin
       ssql:='select * from config where 1='+quotedstr(a[i]);
   end else begin
      ssql:=ssql+' and '+inttostr(i+1)+'='+quotedstr(a[i]);

           end;
end;