PDO and prepared statements on dynamic sized queries - php

Question

I am developing a small gaming website for college fest where users attend few contests and based on their ranks in result table, points are updated in their user table. Then the result table is truncated for the next event. The schemas are as follows:
user
-------------------------------------------------------------
user_id | name | college | points |
-------------------------------------------------------------
result
---------------------------
user_id | score
---------------------------
Now, the first 3 students are given 100 points, next 15 given 50 points and others are given 10 points each.
Now, I am having problem in developing queries because I don't know how many users will attempt the contest, so I have to append that many ? in the query. Secondly, I also need to put ) at the end.
My queries are like
$query_top3=update user set points =points+100 where id in(?,?,?);
$query_next5=update user set points = points +50 where id in(?,?,?,?,?);
$query_others=update user set points=points+50 where id in (?,?...........,?);
How can I prepare those queries dynamically? Or, is there any better approach?
EDIT
Though its similar to this question,but in my scenario I have 3 different dynamic queries.

Answer 1

If I understand correctly your requirements you can rank results and update users table (adding points) all in one query
UPDATE users u JOIN
(
SELECT user_id,
(
SELECT 1 + COUNT(*)
FROM result
WHERE score >= r.score
AND user_id <> r.user_id
) rank
FROM result r
) q
ON u.user_id = q.user_id
SET points = points +
CASE
WHEN q.rank BETWEEN 1 AND 3 THEN 100
WHEN q.rank BETWEEN 4 AND 18 THEN 50
ELSE 10
END;
It totally dynamic based on the contents in of result table. You no longer need to deal with each user_id individually.
Here is SQLFiddle demo