ADO+Access sql查询出错(50分)

with ADOquery1 do
begin
close;
sql.Clear;
sql.Add('select Xm,Dklsh,Hkrq from Hdqk');
sql.Add('where Sb="" or Sb="0.00442500" or Sb="0.00465000"');
open;
end;
查询结果Sb=""数据不在其中,为何?

请改为
with ADOquery1 do
begin
close;
sql.Clear;
sql.Add('select Xm,Dklsh,Hkrq from Hdqk');
sql.Add('where (Sb is null) or (Sb="0.00442500") or (Sb="0.00465000")');
open;
end;

接受答案了.