$query = "SELECT * FROM menus ORDER BY id ASC";
$menus_result = mysql_query($query) or die("Error!");

while( $menu=mysql_fetch_array($menus_result) ) {
   echo $menu['name']."<br />";
}

<?php
$query = "SELECT * FROM menus ORDER BY id ASC";
$menus_result = mysql_query($query);

if ($menus_result)
{
    while( $menu=mysql_fetch_array($menus_result) ) {
       echo $menu['name']."<br />";
    }
}

echo "Next Job";
?>

$query = "SELECT * FROM non_existent ORDER BY id ASC";
$menu_result = mysql_query($query) or NULL;
echo $menu_result;    // Which echoes nothing at all, thus NULL!

if($menu_result == NULL) {
    echo "Yes";
} else {
    echo "No";
}

if ($mysql_result == NULL )

...
function doQuery($sql) {
        return mysql_query($sql, $this->mConn);
    }
...

# the function doQuery() is used in the function called Query!

function Query($sql, $fname = FALSE) {

        $this->mLastQuery = $sql;
        
        # Add a comment for easy SHOW PROCESSLIST interpretation
        if ($fname) {
            $commentedSql = "/* $fname */ $sql";
        } else {
            $commentedSql = $sql;
        }
        
        # Do the query and handle errors
        $result = $this->doQuery($commentedSql);

        # Try reconnecting if the connection was lost
        if (FALSE === $result && ($this->lastErrno() == 2013 || $this->lastErrno() == 2006) ) {
            if ($this->Ping() ) {
                $result = $this->doQuery($commentedSql);
            } else {
                $this->mError = 'MySQL Failure: <b>Connection was lost and reconnecting to the MySQL Server Failed</b>';
                return FALSE;
            }
        }

        if (FALSE === $result) {
            $this->mError = '<b>Fatal Error:</b> Could not <b>' . "/* ". $fname . " */" . '</b> '.$this->lastErrno().': <br /><br /> '.$this->lastError();
            return FALSE;
        }
        return $result;
    }

<?PHP
$query = "SELECT * FROM non_existent";
$menu_result = mysql_query($query) or NULL;

if($menu_result == NULL) {
    echo "Yes";
} else {
    echo "No";
}
?>

<?PHP
$var = NULL;
if(is_null($var)) {
    echo "Yes";
} else {
    echo "No";
}
?>