如何在ASP.NET中使用Access中的JOIN SQL语句？

Question

好吧，我是一名头痛的编程学生，希望有人能够治好。

我目前正在创建使用ASP.NET在Microsoft Visual Studio中的一个网站，一个项目，这里是我的问题：

我在Microsoft Access数据库中包含用户日志中的数据表（姓名，电子邮件，密码）以及包含用户选择的用户安全问题编号（编号是对具有实际问题的ArrayList的引用）以及他们提交的实际答案的链接表。

我正在利用Web服务来处理任何需要访问数据库的东西。

我想要做的是选择数据库中的安全问题编号并返回它的值，但我不确定什么是正确的SQL语句或者我的代码是否允许它工作。所以如果有人能帮助我，我会很感激。请注意，我对编程相当陌生。

这里是我的代码：

//This retrieves the security question of the user. 
[WebMethod] 
public string GetUserQuestion(string email) 
{ 
    try 
    { 
     //Connect to database. 
     this.ConnectToDatabase(); 

     OleDbCommand cmd = conn.CreateCommand(); 

     //The query to return the value of the index of the question that is stored in the arraylist. 
     cmd.CommandText = @"SELECT SecurityInfo.QuestionNumber FROM [SecurityInfo],[UserDetails] WHERE (UserDetails.Email = '" + email + "' JOIN [UserDetails] ON SecurityInfo.ID = UserDetails.ID)"; 

     //cast the value to a string 
     string userQuestion = cmd.ExecuteReader().ToString(); 

     return userQuestion; 

    } 
    catch (Exception e) 
    { 
     return e.ToString(); 
    } 
    finally 
    { 
     this.DisconnectDatabase(); 
    } 
} 

PS：该方法几乎做什么，他们被命名为所以它不应该是必要的，包括他们的问题。

这是在服务中测试这种方法时，我得到的错误：

<string xmlns="http://tempuri.org/"> 
System.Data.OleDb.OleDbException (0x80040E14): Syntax error (missing operator) in query expression '(UserDetails.Email = 'rudivisagiex@gmail.com' JOIN [UserDetails] ON SecurityInfo.ID = UserDetails.ID)'. at System.Data.OleDb.OleDbCommand.ExecuteCommandTextErrorHandling(OleDbHResult hr) at System.Data.OleDb.OleDbCommand.ExecuteCommandTextForSingleResult(tagDBPARAMS dbParams, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommandText(Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommand(CommandBehavior behavior, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior behavior, String method) at System.Data.OleDb.OleDbCommand.ExecuteReader(CommandBehavior behavior) at System.Data.OleDb.OleDbCommand.ExecuteReader() at PTWService.GetUserQuestion(String email) in c:\Users\Rudi\Documents\Visual Studio 2010\WebSites\PTWService\App_Code\PTWService.cs:line 108 
</string> 

我改变了我的代码的（这摆脱了错误，但我仍然没有得到什么，我从数组要）：

//This retrieves the security question of the user. 
[WebMethod] 
public string GetUserQuestion(string email) 
{ 
    try 
    { 
     //Connect to database. 
     this.ConnectToDatabase(); 

     OleDbCommand cmd = conn.CreateCommand(); 

     //The query to return the value of the index of the question that is stored in the arraylist. 
     cmd.CommandText = @"SELECT SecurityInfo.QuestionNumber FROM [SecurityInfo] WHERE (UserDetails.Email = '" + email + "') JOIN [UserDetails] ON SecurityInfo.ID = UserDetails.ID"; 

     //Parse the value to a int 
     int UserQuestionNr = Int32.Parse(cmd.ExecuteReader().ToString()); 

     //Get the question from the array. 
     string Question = (string)questionArray[UserQuestionNr]; 


     return Question; 

    } 
    catch (Exception) 
    { 
     return null; 
    } 
    finally 
    { 
     this.DisconnectDatabase(); 
    } 
} 

因此，如果任何人都可以告诉我，如果我的查询语句是错误的，如何纠正它或者它的其他什么东西完全，我将非常感激。

Answer 1

不知道你在期待什么。你得到的记录太少/很多。

这是我通常期望在Access的SQL代码。

"SELECT SecurityInfo.QuestionNumber 
FROM [SecurityInfo] 
INNER JOIN [UserDetails] 
ON SecurityInfo.ID = UserDetails.ID 
WHERE (((UserDetails.Email) = '" + email + "'));" 

您还应该检查发送到数据库的字符串，以便进行故障排除。

Answer 2

这是解决办法，如果有谁想知道：

[WebMethod] 
public string GetUserQuestion(string email) 
{ 
    try 
    { 
     //Connect to database. 
     this.ConnectToDatabase(); 

     OleDbCommand cmd = conn.CreateCommand(); 

     //The query to return the value of the index of the question that is stored in the arraylist. 
     cmd.CommandText = "SELECT SecurityInfo.QuestionNumber FROM [SecurityInfo] INNER JOIN [UserDetails] ON SecurityInfo.ID = UserDetails.ID WHERE (((UserDetails.Email) = '" + email + "'));"; 

     OleDbDataReader reader = cmd.ExecuteReader(); 

     //Only needs to be read once since only one row will always be returned. 
     reader.Read(); 
     int questionNumber = (int)reader["QuestionNumber"]; 

     //Get the question from the array. 
     string Question = (string)questionArray[questionNumber]; 


     return Question; 

    } 
    catch (Exception) 
    { 
     return null; 
    } 
    finally 
    { 
     this.DisconnectDatabase(); 
    } 
}