There is already an open DataReader associated with this Connection which must be closed

C#There is already an open DataReader associated with this Connection which must be closed
string constr = "Server=.;user=sa;pwd=*********;database=mydb";
        SqlConnection myCon = new SqlConnection(constr);
        try
        {
            using (myCon)
            {
                myCon.Open();
                Console.WriteLine("数据连接已经打开");
                string sql = "select max(age) from mytable003";
                SqlCommand mycommand = new SqlCommand(sql, myCon);
                int t = 0;
                t = (int)mycommand.ExecuteScalar();
                Console.WriteLine("最大年龄是" + t + "岁");
                myCon.Close();
            }

        }
        catch { }
        finally
        {

            myCon.Close();
            Console.WriteLine("数据库已经关闭");
        }
        Console.ReadKey();
这段代码是运行正常的，接下来上面的代码注释掉，运行下面的代码后出现提示：There is already an open DataReader associated with this Connection which must be closed
string constr = "Server=.;user=sa;pwd=*********;database=mydb";
        SqlConnection myCon = new SqlConnection(constr);
      try
        {
            using (myCon)
            {
                myCon.Open();
                string sql = "select * from mytable003";
                SqlCommand mycommand = new SqlCommand(sql, myCon);
                mycommand.ExecuteReader();
                SqlDataReader mydr;
                mydr = mycommand.ExecuteReader();

                if (mydr.HasRows)
                {
                    Console.WriteLine("该表中存在数据");
                }
                else
                {
                    Console.WriteLine("该表中没有数据");
                }
            }

        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message.ToString());
        }
        finally
        {
            myCon.Close();
            Console.WriteLine("数据库已经关闭");
        }

        Console.ReadKey();
所以是第一段代码出现了没有关闭的datareader吗？该怎么处理，网上看了一些东西，但是还是弄不明白，数据库用的是sql server2012

已经使用了using 关键字，不需要再执行close方法
但是你using用错了，应该是
using(SqlConnection myCon = new SqlConnection(constr))
不要把定义放到using外面去
-=-==-
即使你之前的连接没有关闭，也并不影响你建立另一条连接去连数据库，所以跟上一段代码有没有close没有关系
何况你是把程序关闭了，改了代码再重新运行的，那所有占用的资源肯定都释放了，不会有任何影响
我怀疑你代码放的不全，你是不是把第二段代码写循环里了，然后没关闭就又重复执行了myCon.Open();