Question

我在VS2015中使用C＃和MySQl来查询我的数据库。但是，当我输入的列名不是Int或Datetime类型时，datareader会返回错误。

但是，数据库中存在一个列，该列与我输入的字符串作为数据库名称相匹配。我的代码：

        string DateQuery = "SELECT timeStamp, amount, tax, name FROM log.transactions";

        MySqlCommand cmd3 = new MySqlCommand(DateQuery, connectionString);

        MySqlDataReader dataReader3 = cmd3.ExecuteReader();

在编译时，这将返回错误：“mscorlib.dll中发生了'System.Collections.Generic.KeyNotFoundException'类型的未处理异常

附加信息：字典中没有给定的密钥。“

在dataReader3上。

但是如果从查询中删除名称（VarChar类型）列，它将使用timeStamp（DateTime）amount（Int）和tax（Int）编译并执行。

它指的是什么字典不包含密钥？为什么它只影响不是Int或DateTime的类型？

编辑：完整代码发布在下面

 using System;
 using MySql.Data.MySqlClient;

 namespace TestApp
{
 class Program
{
    static void Main(string[] args)
    {
        Program generateReport = new Program();
        generateReport.Kickoff();
    }

    public void Kickoff()
    {
        string dbString = "server=XXXXXX;uid=XXXXXX;" + "pwd=XXXXX;database=XXXXX;";
        MySqlConnection connectionString = new MySqlConnection(dbString);

        connectionString.Open();
        Console.WriteLine("\nAttempting to connect to database...");
        if (connectionString.State.ToString() == "Open")
        {
            Console.WriteLine("Connection successful.");
        }
        else
        {
            Console.WriteLine("Connection failed. :(");
            return;
        }

        string DateQuery = "SELECT timeStamp, amount, tax, name FROM log.transactions";

        MySqlCommand cmd3 = new MySqlCommand(DateQuery, connectionString);
        MySqlDataReader dataReader3 = cmd3.ExecuteReader();
    }
}

}

编辑：Stack Trace我相信：

at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at MySql.Data.MySqlClient.CharSetMap.GetCharacterSet(DBVersion version String CharSetName)
at MySql.Data.MySqlClient.NativeDriver.GetFieldMetaData41()
at MySql.Data.MySqlClient.NativeDriver.GetFieldMetaData()
at MySql.Data.MySqlClient.NativeDriver.ReadColumnMetadata(Int32 count)
at MySql.Data.MySqlClient.MySqlDataReader.NextResult()
at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior       behavior)
at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader()
at TestApp.Program.Kickoff() in c:\users\Testuser\documents\visual studio 2015\Projects\TestApp\TestApp\Program.cs:line 42
at TestApp.Program.Main(String[] args) in c:\users\Testuser\documents\visual studio 2015\Projects\TestApp\TestApp\Program.cs:line 13
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

Answer 1

请尝试使用以下名称：

   SELECT timeStamp, amount, tax,  `name` FROM log.transactions

MySQL查询中缺少键错误

1 个答案: