Order table numerically and get the list number

You can use join for your user table and meta data and order by the meta_value stored in column,

SELECT u.* FROM `wp_users` uJOIN `wp_usermeta` um ON(u.ID = um.`user_id`)WHERE um.`meta_key` = 'reputation'ORDER BY um.`meta_value` * 1 DESC

Using * 1 in order is a simple casting trick to integer and desc will list the user by their reputation score so the user with higher reputation will be listed first and so on

global $wpdb;$query="    SELECT u.*,um.`meta_value` as `rank`     FROM $wpdb->users u    JOIN $wpdb->usermeta um ON(u.ID = um.`user_id`)    WHERE um.`meta_key` = 'reputation'    ORDER BY um.`meta_value` * 1 DESC";$results = $wpdb->get_results($query, OBJECT );

Loop through your results

foreach($results as $r){echo $r->rank; // rank of user}

Edit from comments

here is your function

function getReputationByUser($user_id){    if(!is_numeric($user_id)){    return false;    }    global $wpdb;    $query="    SELECT um.`meta_value` as `rank`        FROM  $wpdb->usermeta um        WHERE um.`meta_key` = 'reputation'        AND um.user_id = '".$user_id."'        ";    $result  = $wpdb->get_row($query);    if(!empty($result)){    return $result->rank;    }    return false;}echo getReputationByUser(100);

Above code is for returning the reputation if you want the rank of user based on reputation you can get this by below query but i am not sure if you can use @variables of Mysql in WPDB class

SELECT t1.`rank`FROM(SELECT   um.user_id,  @rownum:= @rownum + 1 `rank` FROM  wp_usermeta um   CROSS JOIN (SELECT @rownum := 0) t WHERE um.`meta_key` = 'reputation' ORDER BY um.`meta_value` * 1 DESC ) t1WHERE t1.user_id = 100

function for above query

function getReputationByUser($user_id){        if(!is_numeric($user_id)){        return false;        }        global $wpdb;        $query=" SELECT t1.`rank`        FROM(        SELECT          um.user_id,          @rownum:= @rownum + 1 `rank`        FROM          $wpdb->usermeta um          CROSS JOIN (SELECT @rownum := 0) t        WHERE um.`meta_key` = 'reputation'        ORDER BY um.`meta_value` * 1 DESC        ) t1        WHERE t1.user_id = '".$user_id."'";        $result  = $wpdb->get_row($query);        if(!empty($result)){        return $result->rank;        }        return false;}echo getReputationByUser(100);

Here is another way to find the rank for user using group_concat and find_in_set functions

SELECT user_id,FIND_IN_SET(              user_id,(SELECT GROUP_CONCAT( user_id ORDER BY meta_value * 1 DESC)                        FROM `wp_usermeta`                       WHERE meta_key ='reputation')                   ) AS rankFROM wp_usermetaWHERE meta_key ='reputation'AND user_id = 100function getReputationByUser($user_id){        if(!is_numeric($user_id)){        return false;        }        global $wpdb;        $query="SELECT user_id,FIND_IN_SET(                      user_id,(SELECT GROUP_CONCAT( user_id ORDER BY meta_value * 1 DESC)                              FROM $wpdb->usermeta                              WHERE meta_key ='reputation')                           ) AS rank        FROM $wpdb->usermeta        WHERE meta_key ='reputation'        AND user_id = '".$user_id."'        ";        $result  = $wpdb->get_row($query);        if(!empty($result)){        return $result->rank;        }        return false;}echo getReputationByUser(100);

• group_concat

According to docs The result is truncated to the maximum length that is given by the group_concat_max_len system variable, which has a default value of 1024. The value can be set higher, although the effective maximum length of the return value is constrained by the value of max_allowed_packet.