php can't connect to database after using ajax - php

Question

So I'm trying to delete a comment on the website and also from database, but it just works find on web site. After I click delete button, the comment is gone, but nothing changed in my database. After I refresh the page, the comments I deleted appear again.
So I think, somehow, ajax makes php disconnect to MySQL database anymore.
jquery:
$(".delete").each(function (index4) {
$(this).on("click",function (event) {
$(this).parent().parent().load("../public/form/delete_comments.php", {index4:index4}, function () {
$(this).remove();
});
})
php:
<?php
require_once "../../private/initialize.php";
$id = $_SESSION['id'];
$thread_clicked = isset($_POST['index4'])?$_POST['index4']:'';
$req_user = "SELECT * FROM log_in WHERE id='" .$id. "'";
$result_user = mysqli_query($db,$req_user);
$subject_user = mysqli_fetch_assoc($result_user);
$req = "DELETE FROM comments WHERE user=`" .$subject_user['account']. "` AND c_id=`" .$thread_clicked. "`";
$result = mysqli_query($db,$req);
UPDATE: i changed ajax to :$(this).parent().parent().load("/yyqGS/public/form/delete_comments.php",{index4:index4});
but still doesn't do any change to database.
UPDATE:
<?php
require_once "../../private/initialize.php";
session_start();
$id = $_SESSION['id'];
$thread_clicked = isset($_POST['index4'])?$_POST['index4']:'';
$thread_clicked = $thread_clicked +1;
$req_user = "SELECT * FROM log_in WHERE id='.$id.'";
$result_user = mysqli_query($db,$req_user);
$subject_user = mysqli_fetch_assoc($result_user);
$req = "DELETE FROM comments WHERE user='" .$subject_user['account']. "' AND c_id='" .$thread_clicked. "'";
$result = mysqli_query($db,$req);
if ( !$req ) {
printf("Error: %s\n", $mysqli_error($db));
}
else{
echo $result;
}
and i got 1 everytime i delete a comment, but database still doesn't change!
Magic just happened! I don't even know what have I done (I fixed quotation marks problem), but it just works know!
<?php
require_once "../../private/initialize.php";
session_start();
$id = $_SESSION['id'];
$thread_clicked = isset($_POST['index4'])?$_POST['index4']:'';
$thread_clicked = $thread_clicked +1;
$req_user = "SELECT * FROM log_in WHERE id='".$id."'";
$result_user = mysqli_query($db,$req_user);
$subject_user = mysqli_fetch_assoc($result_user);
$req = "DELETE FROM comments WHERE user='" .$subject_user['account']. "' AND c_id='" .$thread_clicked. "'";
$result = mysqli_query($db,$req);
if ( !$req ) {
printf("Error: %s\n", $mysqli_error($db));
}
else{
echo $req;
}
?>

Answer 1

<?php
require_once "../../private/initialize.php";
$id = $_SESSION['id'];
$thread_clicked = isset($_POST['index4'])?$_POST['index4']:'';
$req_user = "SELECT * FROM log_in WHERE id='$id'";
$result_user = mysqli_query($db,$req_user);
$subject_user = mysqli_fetch_assoc($result_user);
$req = $result = mysqli_query($db,$req);
$req = "DELETE FROM comments WHERE user='"$subject_user['account']"' AND c_id='"$thread_clicked"'";
$result = mysqli_query($db,$req);
Try this code for your php. If it works fine i will edit with explanation.

Answer 2

Your using the wrong quotes in your delete statement - your using back ticks which is used to identify fields, not surround values.
$req = "DELETE FROM comments WHERE user=`" .$subject_user['account']. "` AND c_id=`" .$thread_clicked. "`";
should be
$req = "DELETE FROM comments WHERE user='" .$subject_user['account']. "' AND c_id='" .$thread_clicked. "'";
with single quotes rather than backticks.
Edit: It's also useful to check the return values from queries...
if ( !$result ) {
printf("Error: %s\n", $mysqli_error($db));
}
Should let you know if there are any problems with the delete.