variable fails when passing inside a query - php

Question

I am passing the $place variable to a query in listplace.php using a ajax call. The ajax call works perfectly in php1.php code, but the $place value is not passed over the query. Please help!
listplace.php too works perfectly but when i try to pass $place in where condition it fails.
php1.php code
<select id="name">
<option selected disabled>Please select</option>
</select>
<?php if (isset($_GET['place']) && $_GET['place'] != '') { ?>
<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<script>
$.ajax({
type: "POST",
data: {place: '<?= $_GET['place'] ?>'},
url: 'listplace.php',
dataType: 'json',
success: function (json) {
if (json.option.length) {
var $el = $("#name");
$el.empty(); // remove old options
for (var i = 0; i < json.option.length; i++) {
$el.append($('<option>',
{
value: json.option[i],
text: json.option[i]
}));
}
}else {
alert('No data found!');
}
}
});
</script>
<?php } ?>
listplace.php
<?php
//connect to the mysql
$db = #mysql_connect('localhost', 'root', 'password') or die("Could not connect database");
#mysql_select_db('test', $db) or die("Could not select database");
$place = $_POST['place'];
$sql = #mysql_query("select product_name from products_list where product_name = '$place'");
$rows = array();
while($r = mysql_fetch_assoc($sql)) {
$rows[] = $r['product_name'];
}
if (count($rows)) {
echo json_encode(['option'=> $rows]);
}else {
echo json_encode(['option'=> false]);
}
?>

Answer 1

An improvement will be to start using prepared statements. This is just an addition to Exprator's answer
This will prevent SQL injection attacks.
$sql_con = new mysqli('localhost', 'root', 'password', 'test');//get connection
$place = $_POST['place'];//posted variable
if($stmt = $sql_con->prepare("select product_name from products_list where product_name =?")) {//prepare returns true or false
$stmt->bind_param("s", $place); //bind the posted variable
$stmt->execute(); //execute query
$stmt->bind_result($product_name);//bind the result from query securely
$rows = array();//create result array
while ($stmt->fetch()) {//start loop
$rows[] = $product_name;//grab everything in array
}
if (count($rows)) {//check for number
echo json_encode(['option'=> $rows]);
} else {
echo json_encode(['option'=> false]);
}

Answer 2

change this line
data: {place: '<?= $_GET['place'] ?>'},
to
data: {place: '<?= $_GET["place"] ?>'},