html – Add, View, Update and Delete Categories and Subcategories in MySql Php-ThrowExceptions

I have a Table with Columns:

cat_id, cat_name, parent_id

I want to create a page where i can provide the options to add, edit, view and delete categories and Subcategories depending upon each other…

I know how to add categories but i cant add Subcategories with respect to categories. Same is about deleting.

I am using this code to add categories only not sure about the subs:

    <?php
if(isset($_POST["Submit"])){
    $Category=mysqli_real_escape_string($Connection,$_POST["Category"]);
    date_default_timezone_set("Asia/Karachi");
    $CurrentTime=time();
    $DateTime=strftime("%B - %d, %Y at %H:%M:%S", $CurrentTime);
    $DateTime;
    $Admin="Sajid Mukhtar";
    if(empty($Category)){
        $_SESSION["ErrorMessage"]="All Fields must be filled out";
        Redirect_to("managecategories.php");
    }elseif(strlen($Category)>99){
        $_SESSION["ErrorMessage"]="Too long for a category name...";
        Redirect_to("managecategories.php");
    }else{
        global $Connection;
        $Query="INSERT INTO category (datetime,name,creatorname) VALUES ('$DateTime','$Category','$Admin')";
        $Execute=mysqli_query($Connection,$Query);
        if($Execute){
            $_SESSION["SuccessMessage"]="Category Added Successfully.";
        Redirect_to("managecategories.php");
        }else{
            $_SESSION["ErrorMessage"]="category failed to Add";
        Redirect_to("managecategories.php");
        }
    }
}

?>

If someone can help me with the code, I will be very grateful…
Just PHP and SQL Code is requested…
Thanks in advance…

Sajid