How do I get multiple rows of data with PHP using Mysql, send it JSON encoded with ajax, and then read it with javascript/jquery

I am pretty new to combining codes so I need some help. I want to grab the comments for a particular article and put them on the webpage. I can do this when I just find 1 row, but I don't know how to grab multiple rows of data from a database using PHP, JSON encode it, then grab it with ajax, decode it and loop through the rows with javascript on the main page.

When I do the PHP code by itself it shows "{"ID":"1","comment":"this is the first comment"}{"ID":"2","comment":"this is the second comment"}{"ID":"3","comment":"this is the third comment"}" I don't know if this is the proper format for the javascript to read it.

I also, never get to the alerts in the javascript.

Thanks for your help.

/*****************here is javascript that I've been using on index.html*******************************/
 
$.getJSON('../advice/php/get_comments.php', ' ', process_comments);
function process_comments(data) {
var new_comment = data.comment;
var ID = data.ID;
alert('new_comment'+ new_comment);
alert('ID'+ID);
}
 
 
 
 
/*****************here is get_comments.php*******************************/
 
<?PHP
include("../../php/mysql.php"); //gets the mysql info.
 
 
 
$get_comments_sql = "SELECT ID, comment
					FROM comments
					WHERE ID = articles_ID = 47
					GROUP BY ID";
		if ($result = mysqli_query($mysqli, $get_comments_sql)) {
			while ($row = mysqli_fetch_array($result)) {
				$array_data = array('ID'=>$row[0], 'comment'=>$row[1]);
				echo json_encode($array_data);
			}
		}
?>

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