Calculation of Points in a Database in 3rd NF - php

Question

I have a database where the results from a shooter game are stored. I put them to 3NF to allow extensions of the system. So it looks like this:
Player
-------------------
GameId integer
PlayerId integer
TeamId integer
Hits
-------------------
GameId integer
FromId integer
ToId integer
Hits integer
So basically for every game there is a ID and every Player and Team has its ID (with their names stored in other databases)
Now I want to calculate points for each player. I need the points for each game but more importantly the total per player. The points are basically: 3 Points for each hit on opponent, -2 points for each hit of a team member and -2 points for each hit taken.
Alone the calculation of the number of team hits requires a JOIN with 3 tables and I fear for performance in production environment. (Each game has ~8 players-> PlayerDB-Size is 8n and HitsDB-Size is (8-1)^2*n)
And at the end: I need to calculate the points per player for each game and sum those up because the minimum points per game should be zero. And finally get a rank for each player (player x has the 2nd most total points etc)
I feel like I'm getting lost in overly complicated queries that will kill the database' performance at some point.
Could anyone judge the design and maybe give me some pointers where to start looking further? I though about storing the TeamHits and Points per Game in the players Database (Points for summing over them, teamHits for statistical purposes) but that would of course break normalization.
PS: I'm working with PHP 5 and MYSQL. I also thought about getting each game from the database, calculating the points in PHP (which I'm already doing when I show the game) and writing this back (optimally on putting in the game to the DB but also when the parameters for the points change)
Edit: Idea to avoid subselects would be:
SELECT p.*, SUM(h.Hits) AS TeamHits, SUM(h2.Hits) as Hits
FROM player p
LEFT JOIN
(hits h
INNER JOIN player p2
ON h.GameId=p2.GameId AND h.ToId=p2.PlayerId
)
ON p.GameId=p2.GameId AND h.FromId=p.PlayerId AND p.TeamId=p2.TeamId
GROUP BY p.PlayerId, p.GameId
LEFT JOIN hits h2
ON h2.GameId=p.GameId AND h2.FromId=p.PlayerId
But of course this does not work. Is it even possible to combine groupings with joins or will I have to use subqueries?
Best I have is:
SELECT p.PlayerId, SUM((-2-3)*IFNULL(th.TeamHits, 0) + (3)*IFNULL(h.Hits, 0) + (-2)*IFNULL(ht.HitsTaken, 0)) AS Points
FROM player p
LEFT JOIN
(SELECT p.GameId, p.PlayerId, SUM(h.Hits) AS TeamHits
FROM player p
INNER JOIN hits h
ON h.GameId=p.GameId AND p.PlayerId=h.FromId
INNER JOIN player p2
ON p.GameId=p2.GameId AND p2.PlayerId=h.ToId AND p.TeamId=p2.TeamId
GROUP BY p.PlayerId, p.GameId) th
ON p.GameId=th.GameId AND p.PlayerId=th.PlayerId
LEFT JOIN
(SELECT p.GameId, p.PlayerId, SUM(h.Hits) AS Hits
FROM player p
INNER JOIN hits h
ON h.GameId=p.GameId AND p.PlayerId=h.FromId
GROUP BY p.PlayerId, p.GameId) h
ON p.GameId=h.GameId AND p.PlayerId=h.PlayerId
LEFT JOIN
(SELECT p.GameId, p.PlayerId, SUM(h.Hits) AS HitsTaken
FROM player p
INNER JOIN hits h
ON h.GameId=p.GameId AND p.PlayerId=h.ToId
INNER JOIN player p2
ON p.GameId=p2.GameId AND p2.PlayerId=h.FromId AND p.TeamId!=p2.TeamId
GROUP BY p.PlayerId, p.GameId) ht
ON p.GameId=ht.GameId AND p.PlayerId=ht.PlayerId
GROUP BY p.PlayerId
Fiddle: http://sqlfiddle.com/#!9/dc0cb/4
Current problem: For a database with about 10,000 games calculating the points for all players takes about 18s. This is unusable, so I need to improve this...

Answer 1

Joins are not that expensive, subqueries are. as long as you can avoid subqueries you're not hitting too bad.
Remember, a database is built for this stuff these days.
Just make sure you have the proper indexes on the right fields so its optimised. Like teamID and GameID and playerID should be indexes.
Just run it in phpmyadmin and see how many milliseconds it takes to execute. if it takes more than 50 its a heavy query, but usually its pretty hard to hit this... I once managed to make a very heavy query that joined 100.000+ rows out of different tables and views and still did that in 5ms...
What numbers of requests a hour are we talking about? 200 players a day? 200.000 players a day? How often do the requests happen? 10 per second per player? once a minute? how loaded is your database?
I think that all these parameters are low, so you shouldnt worry about this optimisation yet.
Get your game up and running, clean up the php code where real gains can be had, and stay clear of complex subqueries or views.
As long as your table does joins and unions its pretty darn fast. and if you must do a subquery see if there is not an alternative way by using a linking table to link certain results to certain other tables so you can do a join instead of a subquery.