Dependent category subcategory dropdown in PHP, MySQL & Ajax

[@AdTechAcademy-fe3tr]

its works for my project thanks a ton

[@gauritechnical]

bro this is very helpful video for me....

[@rogerp.catamcojr.8483]

I LIKE HOW YOU TEACH

[@computerlearningbyargusaca5217]

🙏🙏Very nice . love to see more 👍👍videos . 😍😍 thanks for uploading👌👌

[@TechRudranshi]

Love you too bro

[@MdMozid-vr9iw]

Hello sir, this is nice tutorial. I need your help sir can you please make a tutorial on dynamic dropdown list crud operation project using php mysql and ajax.

[@laboptyka3706]

Super! Thank You!

[@parteekkumar742]

Thanks for video

[@er.sanjeet7711]

hlo r u thare

[@DavidAshby1]

Hi, I have goe through the video and am having a problem with the sub category query. When I echo the sub cat query it gives me
SELECT * FROM categories WHERE parent_id =
the query in get_subcat.php is
$sql = "SELECT * FROM categories WHERE parent_id = $category_id";
$result = mysqli_query($conn, $sql);
The category dropdown is populated but the sub category isn't populating.
I am getting 1 notice and 1 warning
Notice: Undefined index: category_id in C:\xampp\htdocs\dependantdropdown2021\dependantdropdown2\get_subcat.php on line 4
Select Sub Category
Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\dependantdropdown2021\dependantdropdown2\get_subcat.php on line 14
SELECT * FROM categories WHERE parent_id =
could you advise please?
I also copied and pasted your code into my files but still have the same issues.
Notice: Undefined index: category_id in C:\xampp\htdocs\dependantdropdown2021\dependantdropdown2\get_subcat.php on line 3
Select Sub Category
Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\dependantdropdown2021\dependantdropdown2\get_subcat.php on line 8
Thanks