Store mysql column to array PHP

$result is empty and $query is not used anywhere.

You need something like this:

$result = mysql_query($query);

http://php.net/manual/en/function.mysql-query.php

Your code is not correct. You didn't execute the query. You need to do this :

mysql_connect("localhost", "xxxx", "xxxx") or die ("Not connected");
mysql_select_db("xxxxx") or die ("no database");

$result_array = array();
$query = mysql_query("SELECT xxxx_device_token FROM device_tokens");

while($row = mysql_fetch_assoc($query))
{
    $result_array[] = $row['xxxx_device_token'];
}
print_r($result_array);

But mysql_query is deprecated in new verion of PHP, so you need to do this with mysqli_query.

Try this,

$query = "SELECT xxxx_device_token FROM device_tokens";
$result = mysql_query($query);


$result_array = array();
while($row = mysql_fetch_assoc($result))
{
    $result_array[] = $row['xxxx_device_token'];
}

Dont use Mysql functions. It is deprecated. Please move to Mysqli (or) PDO

You have mysql_fetch_assoc($result) in the while statement, but no variable declaration for $result.

You must execute your query:

$result = mysql_query($query);

Assuming this is not a copy & paste error, you are probably missing this line:

$result = mysql_query($query);

Try not to use mysql_*, it's not recommended, use mysqli_* , ideally you should be using PDO for database connectivity.

That said you're missing this, $result = mysql_query($query);

You have forgotten to execute your MySQL query, like this:

$result = mysql_query($con,"SELECT * FROM Persons");