只允许ajax请求触发一次（如按钮）

I have a button that on click adds 1 to a table value in my database (i.e a like button).

When the user clicks the button:

  var button_id = $(e.target).closest('div').attr('id');
  var id = button_id.substring(12);
  $.ajax({
    method: 'POST',
    url: 'update_like.php',
    data: {id:id},
    success: function(){
     //
    },
    error: function(){
      //
    }
  }) 

update_like.php

$id = mysqli_real_escape_string($conn,$_POST['id']);

if (!empty($_POST)){
    mysqli_query($conn,"UPDATE posts SET likes=likes+1 WHERE id='$id'");
}

Q: What way can it check if they already liked it, so that they can only like the post once?

I just thought of something like this:

Have a column called "likers" or something similar, with a long list of user IDs who've liked the post.

i.e.

5 217 16 31893 ... <-- user IDs

In update_like.php, check if the user who's logged in's ID can be found within that string. Something like:

$id = mysqli_real_escape_string($conn,$_POST['id']);

$result = mysqli_query($conn,"SELECT likers FROM posts WHERE id='$id'");
$likers = mysqli_fetch_assoc($result);
$user_id = $_SESSION['id']; // user ID

if (!empty($_POST)){
    if (!(preg_match("/\b$user_id\b/", $likers))){
        mysqli_query($conn,"UPDATE posts SET likes=likes+1 WHERE id='$id'");
    }
}

Is this feasible?

You can try this:

var button_id = $(e.target).closest('div').attr('id');
var id = button_id.substring(12);
var idArray = [];
if (idArray.indexOf(id) === -1) {
 ajaxCall = $.ajax({
    method: 'POST',
    url: 'update_like.php',
    data: {id:id},
    success: function(){
     //
      idArray.push(id);
    },
    error: function(){
      //
    }
  });
}

On server side you can try this: Assuming ID to be a comma separated list.

UPDATE posts 
SET likes = likes+1 
WHERE id = '$id'
AND FIND_IN_SET('$id', listofuserid) = 0