MySQL connection within a PHP function overwrites existing connection (other database) - how can I prevent this?

Question

We open a MySQL connection to host_1 at the beginning of our script. Somewhere in between, we call a function that opens & closes a connection to host_2 (function retrieve_information_from_host_2).

Unfortunately, the code after the function call still uses the connection of the function (host_2).

We need it though to continue with the preceding connection host_1.

<?php

function retrieve_information_from_host_2($host_2, $username_2, $password_2, $database_2) {
    $connection = mysql_connect($host_2, $username_2, $password_2);
    if($connection) {
        if(mysql_select_db($database_2)) {
            $sql = "SELECT * FROM table WHERE id = 1;";
            $erg = mysql_query($sql);
            $row = mysql_fetch_assoc($erg);

            return $row;
        }
        mysql_close($connection);
    }
}

if(mysql_connect($host_1, $username_1, $password_1)) {
    if(mysql_select_db($database_1)) {
        $sql = "SELECT * FROM table WHERE id = 1;";
        $erg = mysql_query($sql);
        $row = mysql_fetch_assoc($erg); # CORRECT - This returns data from host 1

        $row_host_2 = retrieve_information_from_host_2(); # CORRECT - This returns data from host 2

        $sql = "SELECT * FROM table WHERE id = 2;";
        $erg = mysql_query($sql);
        $row = mysql_fetch_assoc($erg); # WRONG - This returns data from host 2 instead of host 1
    }
    mysql_close();
}
?>

We have tried almost every combination by giving each connection a name

$connection_1 = mysql_connect($host_1, $username_1, $password_1);
...
mysql_close($connection_1);

and closing them explicitly, etc.

Nothing helps. Can someone give us a solution to this problem?

PS: We are bound to this approach (functions) and can't use classes.

Thank you very much!

Answer 1

Try to pass your connection link identifier as second argument.

For example:

$connection1 = mysql_connect($host_1, $username_1, $password_1);
$connection2 = mysql_connect($host_2, $username_2, $password_2);
mysql_query('Query',$connection1);
mysql_query('Query',$connection2);

Answer 2

See manual for mysql_query for second parameter link_identifier (The MySQL connection)

If the link identifier is not specified, the last link opened by mysql_connect() is assumed.

You also should use mysqli instead of the old mysql.