Help limiting inner join

I need help limiting inner join.

Tables:

---

users:

• uid
• left
• active

---

files:

• fid

---

uid=fid

---

SELECT uid
FROM users AS u
INNER JOIN files AS x ON u.uid = x.fid
WHERE u.left = '0'
AND u.active = '1'
ORDER BY `u`.`uid` ASC

result:

uid
3
3
3
3
7
47
47
47
47
47
47
47
47
47
47

I need to limit INNER JOIN to 5 . so "uid" will not show up more than 5 times. like:

uid
3
3
3
3
7
47
47
47
47
47

---

update:

Here is the php code

 $res = do_sqlquery("SELECT uid FROM users as u INNER JOIN files as x ON u.fid=x.fid WHERE u.left = '0'  AND u.active='1'");
   if (mysql_num_rows($res) > 0)
   {
       while ($arr = mysql_fetch_assoc($res))
       {
       $x=$arr["uid"];
       quickQuery("UPDATE users SET pots = pots+".$GLOBALS["bui"]."*"开发者_如何学JAVA.$cleaint."/900 WHERE id = '$x'");
       }
   }

---

A MySQL only solution, without using PHP

SELECT uid
from (
    SELECT u.uid, @r:= if(@u=u.uid,@r+1,1) r, @u:=u.uid
    FROM users AS u
    CROSS JOIN (select @u:=null) g
    INNER JOIN files AS x ON u.uid = x.fid
    WHERE u.`left` = '0'
    AND u.active = '1'
    ORDER BY u.uid ASC
) U
WHERE U.r <= 5
ORDER BY uid ASC

or more generally, just SQL without MySQL variables

SELECT u.uid
from (
    SELECT u.uid, count(*) C
    FROM users AS u
    INNER JOIN files AS x ON u.uid = x.fid
    WHERE u.`left` = '0'
    AND u.active = '1'
    GROUP BY u.uid
) U inner join (
   select 1 n union all select 2 union all select 3
    union all select 4 union all select 5) V ON U.C>=V.n
ORDER BY U.uid ASC

---

In MySQL:

SELECT CONCAT(`uid`, ":", MAX(5, COUNT(`fid`))) `uid_count`
FROM ...
GROUP BY `uid`

Gives you results like:

uid_count
3:4
7:1
47:5

In PHP, for example, you can then split after fetching:

while (FALSE !== ($row = mysql_fetch_assoc($query))) {
    ($uid, $count) = split(':', $row['uid_count'], 2);
}