「命令執行過程中遇到致命錯誤」 我使用SET和SELECT XXX FROM（SELECT XXX FROM XXX）

Question

我有這樣的代碼：

Function Get_Control_Station_Address(counter As Integer) 
    Check_DB_Con() 'Check if the connection is okay 
    SQL_Query = "SET @row_number = 0; " _ 
       & "SELECT hardware_add " _ 
       & "FROM (" _ 
        & "SELECT " _ 
        & "@row_number:=@row_number + 1 AS num, " _ 
        & "hardware_add AS hardware_add " _ 
        & "FROM teller_info" _ 
       & ") AS sub_query " _ 
       & "WHERE num = " & counter & ";" 

    Dim MySQL_CMD As New MySqlCommand(SQL_Query, MysqlConn) 

    Try 
     MySQL_CMD.Connection.Open() 
     MySQL_Reader = MySQL_CMD.ExecuteReader() 

     While MySQL_Reader.Read 
      MySQL_Result = MySQL_Reader("hardware_add") 
     End While 

     Return MySQL_Result 
     MySQL_Reader.Close() 
    Catch myerror As MySqlException 
     Console.WriteLine("Failed to run query: " & myerror.Message) 
     Return Nothing 
    Finally 
     MysqlConn.Close() 
     MysqlConn.Dispose() 
    End Try 
End Function 

我收到此錯誤：

A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
A first chance exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll 
Failed to run query: Fatal error encountered during command execution. 

我確信有no basic errors在這裏像database connection error，作爲一個證明我有這個功能，我100％肯定工作，它是幾乎相同的前一個功能不工作，唯一的區別是查詢。

Function Get_Control_Station_Total() 
    Check_DB_Con() 'Check if the connection is okay 
    SQL_Query = "SELECT COUNT(*) AS total_count FROM teller_info" 
    Dim MySQL_CMD As New MySqlCommand(SQL_Query, MysqlConn) 

    Try 
     MySQL_CMD.Connection.Open() 
     MySQL_Reader = MySQL_CMD.ExecuteReader() 

     While MySQL_Reader.Read 
      MySQL_Result = MySQL_Reader("total_count") 
     End While 

     Return MySQL_Result 
     MySQL_Reader.Close() 
    Catch myerror As MySqlException 

     Return ("Failed to run query: " & myerror.Message) 
    Finally 
     MysqlConn.Close() 
     MysqlConn.Dispose() 
    End Try 
End Function 

因此，仔細觀察問題，看起來這個代碼是錯誤的根源。

SQL_Query = "SET @row_number = '0'; " _ 
       & "SELECT hardware_add " _ 
       & "FROM (" _ 
        & "SELECT " _ 
        & "@row_number:=@row_number + 1 AS num, " _ 
        & "hardware_add AS hardware_add " _ 
        & "FROM teller_info" _ 
       & ") AS sub_query " _ 
       & "WHERE num = '" & counter & "';" 

其實我重新創建直接使用heidiSQL該查詢，它工作的偉大，讓我有點困在這裏，也許我使用SET @row_number = '0';錯了嗎？

總結：

1. 我敢肯定，這不是MySQL連接問題
2. 我相信，MySQL的查詢工作（通過測試它直接在HeidiSQL）
3. 過程獲取數據似乎工作，因爲我只是複製它從一個工作函數獲取數據的方式。

編輯：遵循@評論console.writeline的Ken_White的評論我能夠清楚地看到錯誤

這裏的錯誤

MySql.Data.MySqlClient.MySqlException (0x80004005): Fatal error encountered during command execution. ---> MySql.Data.MySqlClient.MySqlException (0x80004005): Parameter '@row_number' must be defined. 
    at MySql.Data.MySqlClient.Statement.SerializeParameter(MySqlParameterCollection parameters, MySqlPacket packet, String parmName, Int32 parameterIndex) 
    at MySql.Data.MySqlClient.Statement.InternalBindParameters(String sql, MySqlParameterCollection parameters, MySqlPacket packet) 
    at MySql.Data.MySqlClient.Statement.BindParameters() 
    at MySql.Data.MySqlClient.PreparableStatement.Execute() 
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior) 
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior) 
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader() 
    at TCP_Client.Module_Database.Get_Control_Station_Address(Int32 counter) in C:\Users\xxxxx\xxx.vb:line 198 

Answer 1

看來，通過加入Allow User Variables = True我數據庫連接解決了我的問題。

所以不是

Public Sub Check_DB_Con() 
    'Declare database credentials so we can refresh it in recheck timer 
    server = My.Settings.DB_Server 
    username = My.Settings.DB_Username 
    password = My.Settings.DB_Password 
    database = My.Settings.DB_Database 

    'Connection String 
    MysqlConn.ConnectionString = "server=" & server & ";" _ 
    & "user id=" & username & ";" _ 
    & "password=" & password & ";" _ 
    & "database=" & database 
End Sub 

我添加Allow User Variables=True，因此，它將成爲

Public Sub Check_DB_Con() 
    'Declare database credentials so we can refresh it in recheck timer 
    server = My.Settings.DB_Server 
    username = My.Settings.DB_Username 
    password = My.Settings.DB_Password 
    database = My.Settings.DB_Database 

    'Connection String 
    MysqlConn.ConnectionString = "server=" & server & ";" _ 
    & "user id=" & username & ";" _ 
    & "password=" & password & ";" _ 
    & "database=" & database & ";Allow User Variables=True" 
End Sub 

Answer 2

而是在2個步驟設置SQL RN的價值，使用交叉連接。我不認爲這個電話會正確處理這兩個陳述。

SQL_Query = "SELECT hardware_add " _ 
      & "FROM (" _ 
       & "SELECT " _ 
       & "@row_number:=@row_number + 1 AS num, " _ 
       & "hardware_add AS hardware_add " _ 
       & "FROM teller_info" _ 
       & "CROSS JOIN (SELECT @row_number:=0) AS t " _ 
      & ") AS sub_query " _ 
      & "WHERE num = '" & counter & "';" 

堆棧示例：ROW_NUMBER() in MySQL