无法在本地数据库上发送/写入数据

 <?php
      if (isset($_POST["Submit"])) {
      $Category = mysqli_real_escape_string($Connection, $_POST["Category"]);
      date_default_timezone_set("Asia/Tokyo"); 
      $CurrentTime = time();
      $DateTime = strftime("%d-%Y %H:%M:%S", $CurrentTime);
      $DateTime;
      $Admin = "XYZ";
      if (empty($Category)) {
      $_SESSION["ErrorMessage"] = "All Fields must be filled out!";
      Redirect_to("Categories.php");
      } elseif (strlen($Category) > 99) {
      $_SESSION["ErrorMessage"] = "Too long name!";
      Redirect_to("Categories.php");
      } else {
      //the issue occurs below this...

      global $ConnectingDB;                           //$ConnectingDB selects the database
      $Query = "INSERT INTO category(datetime,name,creatorname)
      VALUES('$DateTime','$Category','$Admin')";
      $Execute = mysqli_query($Connection, $Query);   //$Connection is the link
      if ($Execute) {
          $_SESSION["SuccessMessage"] = "Categories Added Successfully!";
          Redirect_to("Categories.php");
     } else {
        $_SESSION["ErrorMessage"] = "Category failed to add!";
        Redirect_to("Categories.php");
     }
     }
     }

    ?>
      //the form code...
     <form action="Categories.php" method="POST">
                    <fieldset>
                        <div class="form-group">
                            <label for="categoryname">Name:</label>
                            <input type="text" class="form-control" name="Category" id="categoryname" 
                        placeholder="Name">
                        </div>
                        <input class="btn btn-default" type="Submit" name="Submit" 
                    value="Add New Category">
                    </fieldset>
                </form>

问题：当我输入类别名称并将其提交到数据库时，该查询未在我的数据库（phpmyadmin）中写入新条目。该页面上显示的警报消息是“类别添加失败”。我应该如何解决这个问题？我只有4列：ID，日期时间，名称，创建者名称。

db.php：

 <?php
      $Connection = mysqli_connect('localhost', 'root', '');
      if (!$Connection) {
      die("Database connection failed: " . mysqli_connect_error());
      }


       $ConnectingDB = mysqli_select_db($Connection, 'myblog');
       if (!$ConnectingDB) {
       die("Database selection failed: " . mysqli_connect_error());
       }

$ _SESSION消息：

<?php 
   function Message () {
   if (isset($_SESSION["ErrorMessage"])) {
    $Output="<div class=\"alert alert-danger\">";
    $Output.=htmlentities($_SESSION["ErrorMessage"]);
    $Output.="</div>";
    $_SESSION["ErrorMessage"]=null;
    return $Output;
    }
    }
    function SuccessMessage () {
    if (isset($_SESSION["SuccessMessage"])) {
    $Output="<div class=\"alert alert-success\">";
    $Output.=htmlentities($_SESSION["SuccessMessage"]);
    $Output.="</div>";
    $_SESSION["SuccessMessage"]=null;
    return $Output;
    }
   }
   ?>

   //this is to display the success message in managing categories
   <div><?php echo Message(); echo SuccessMessage(); ?></div>

我是PHP的初学者。