$res = mysql_query("SELECT `id` FROM `table1`");//Смотрим какие есть айдишки.
$arr = array();
 
while($rows = mysql_fetch_row($res)){
 
    $arr[] = $rows[0];
    echo $rows[0];
}


$r = mysql_query("SELECT COUNT(*) FROM `table1`
                  WHERE `id` =".$rows[0]."");//Считаем количество строк в которых есть совпадения по айдишкам.

 
while($row = mysql_fetch_row($r)){
 
    
    echo $row;
}

$res = mysql_query("SELECT COUNT(user_id) FROM table1
                                           WHERE user_id =(SELECT user_id FROM table2);
                                           while($rows = mysql_fetch_row($res)){
                                           $arr = array();
                                           $arr[] = $rows[0];
                                          
                                           $que = mysql_query("UPDATE table1 SET score =".$arr[]." WHERE user_id =(SELECT user_id FROM table2));
                                           }

$res = mysql_query("SELECT COUNT(user_id) FROM table2
                                           WHERE user_id =(SELECT user_id FROM table1);
                                           while($rows = mysql_fetch_row($res)){
                                           $arr = array();
                                           $arr[] = $rows[0];
                                          
                                           $que = mysql_query("UPDATE table1 SET score =".$arr[]." WHERE user_id =(SELECT user_id FROM table2));
                                           }

$sql = <<<SQL
SELECT 
    COUNT( `table2`.`user_id` ) AS `count_id` , 
    `table2`.`user_id` AS `user_id`
FROM 
    `table1`
JOIN 
    `table2` ON `table2`.`user_id` = `table1`.`user_id`
GROUP BY 
    `table2`.`user_id`
SQL;


$res = mysql_query($sql);
while($row = mysql_fetch_assoc($res)) {
    $sql = "UPDATE `table1` SET `score`={$row['count_id']} WHERE `user_id`={$row['user_id']}";
    mysql_query($sql);
}

$res = mysql_query("SELECT `int`,`score` FROM `table1`");
$arr = array();

while($rows = mysql_fetch_assoc($res))
$arr . = $rows['score'] / $rows['int'];
 {
    $sql = "UPDATE `table1` SET `score`={$arr .} WHERE `user_id`={$row['user_id']}";
    mysql_query($sql);

}

$sql = <<<SQL
SELECT 
    COUNT( `table2`.`user_id` ) AS `count_id` , 
    `table2`.`user_id` AS `user_id`
FROM 
    `table1`
JOIN 
    `table2` ON `table2`.`user_id` = `table1`.`user_id`
GROUP BY 
    `table2`.`user_id`
SQL;

SELECT t.cnt/tbl1.int, t.uid FROM (
	SELECT count(*) as cnt, user_id as uid from ...
) t, table1 tbl1
WHERE tbl1.user_id = t.uid

...или так

SELECT t.cnt/t.int, t.uid FROM (
	SELECT count(*) as cnt, table1.user_id as uid, table1.int from ...
	GROUP BY 2,3
) t

$sql = <<<SQL
SELECT 
    COUNT( `table2`.`user_id` ) AS `count_id` , 
    `table2`.`user_id` AS `user_id`
FROM 
    `table1`
JOIN 
    `table2` ON `table2`.`user_id` = `table1`.`user_id`
GROUP BY 
    `table2`.`user_id`
SQL;