從SQL數據庫檢索空值和其他值到文本框

Question

我在從Visual Studio中的SQL數據庫中檢索值時遇到問題。我在GUEST表中有列（GuestName，GuestPassportNo，GuestCountry，RoomID，HotelPackageID），其中HotelPackageID包含一個NULL值，其餘值都是值。當HotelPackageID爲NULL時，我總是被拋入else語句（找不到記錄）。任何人都有解決方法嗎？這裏是我的代碼：

SqlConnection myConnect = new SqlConnection(strConnectionString); 

string strCommandText = "SELECT Guest.GuestPassportNo, 
           Guest.GuestName, 
           Guest.GuestCountry, 
           Guest.RoomID, 
           Room.RoomDescription, 
           Room.RoomPrice, 
           HotelPackages.PackageName, 
           HotelPackages.PackagePrice "; 

strCommandText += " FROM Guest, Room, HotelPackages"; 

strCommandText +=" WHERE Guest.RoomID=Room.RoomID 
        AND Guest.GuestPassportNo=@guestpno 
        AND HotelPackages.PackageID=Guest.HotelPackageID 
        AND Guest.GuestCountry=@guestcountry; 

SqlCommand cmd = new SqlCommand(strCommandText, myConnect); 
cmd.Parameters.AddWithValue("@guestpno", txtPassportNo.Text); 
cmd.Parameters.AddWithValue("@guestcountry", txtGuestCountry.Text); 

try 
{ 
myConnect.Open(); 
SqlDataReader reader = cmd.ExecuteReader(); 

if(reader.Read()) 
{ 
txtGuestName.Text = reader["GuestName"].ToString(); 
txtRoomDescription.Text = reader["RoomDescription"].ToString(); 
txtRoomPrice.Text = reader["RoomPrice"].ToString(); 
txtHotelPackage.Text = reader["PackageName"].ToString(); 
txtPackagePrice.Text = reader["PackagePrice"].ToString(); 
MessageBox.Show("Guest Record Found!"); 
} 

else 
{ 
Messagebox.Show("No record Found"); 
} 

reader.Close(); 
} 

catch(Exception ex) 
{ 
MessageBox.Show(ex.message); 
} 

finally 
{ 
myConnect.Close(); 
} 

Answer 1

您需要更改您的查詢：

strCommandText +=" WHERE Guest.RoomID=Room.RoomID AND Guest.GuestPassportNo=@guestpno AND HotelPackages.PackageID=Guest.HotelPackageID AND Guest.GuestCountry=@guestcountry; 

應該是：

strCommandText +=" WHERE Guest.RoomID=Room.RoomID AND Guest.GuestPassportNo=@guestpno AND (HotelPackages.PackageID=Guest.HotelPackageID OR GUEST.HotelPackageID IS NULL) AND Guest.GuestCountry=@guestcountry;