Access denied for user ''@'localhost' (using password: NO) [duplicate]

Answer 1

This warning will be logged anytime you try to execute a query without a valid connection object being available.

In your case you thought you had a valid connection object available, but you created it using mysqli while your query is being executed using mysql. Those are two different APIs and so the mysql_query function was looking for a mysql connection object and didn't find it.

Answer 2

This is because you create a connection using mysqli_ and then use mysql_ to try to fetch your result. They are different API's.

<?php
$link = mysqli_connect('localhost', 'my_user', 'my_password', 'my_db');

if (!$link) {
    die('Connect Error (' . mysqli_connect_errno() . ') '
            . mysqli_connect_error());
}

echo 'Success... ' . mysqli_get_host_info($link) . "\n";

mysqli_close($link);
?>

See the manual