Need help calculating wins and losses from points scored

Question

I am creating a website in php to log ping pong scores for my school, and currently the player who wins will log the WinnerID, LoserID, PointsFor, PointsAgainst. I have two tables with the following relationships.

Table: users

• user_ID (PK)
• username
• Elo

Table: games

• game_id (PK)
• WinnerID (FK)
• LoserID (FK)
• PointsFor
• PointsAgainst

My insert statement in the php file is:

INSERT INTO games(WinnerID,LoserID,PointsFor,PointsAgainst) VALUES('$Winner_ID','$Loser_ID','$userscore','$oppscore')"

Here is what I have tried, but it doesn't display the scores correctly.

SELECT min(u.username) 'Username', COUNT(g.WinnerID) 'Wins', sum(g.PointsFor) 'Points For', sum(g.PointsAgainst) 'Points Against', u.Elo 'Ranking' 
from games g 
LEFT JOIN users u 
on g.WinnerID = u.user_id 
Group by g.WinnerID

As you can see by the image above, the points for and points against totals don't add up. Currently, it only displays the stats for whoever was winner. Meaning if PlayerA wins 21-5, it will show up from the select statement, but PlayerB will not show a score of 5-21. Any help is appreciated.

PHP code for page to enter scores:

if(isset($_POST['btn-post']))
{
    $opponent = $_POST["opponent"];
    //$opponent = array_key_exists('opponent', $_POST) ? $_POST['opponent'] : false;

    $userscore = mysql_real_escape_string($_POST['userscore']);
    $oppscore = mysql_real_escape_string($_POST['oppscore']);

    if($userscore != $oppscore)
    {
        if($userscore > $oppscore)
        {
            $Winner_ID = $_SESSION['user'];
            $query = mysql_query("SELECT user_id FROM users WHERE username = '".$opponent."'");
            $result = mysql_fetch_array($query) or die(mysql_error());
            $Loser_ID = $result['user_id'];

            $query1 = mysql_query("SELECT Elo FROM users WHERE user_id=".$_SESSION['user']);
            $result1 = mysql_fetch_array($query1) or die(mysql_error());
            $winnerRating = $result1['Elo'];

            $query2 = mysql_query("SELECT Elo FROM users WHERE user_id=".$Loser_ID);
            $result2 = mysql_fetch_array($query2) or die(mysql_error());
            $loserRating = $result1['Elo'];

            $rating = new Rating($winnerRating, $loserRating, 1, 0);            
            $results = $rating->getNewRatings();

            if(mysql_query("UPDATE users SET Elo = " . $results['a'] . " WHERE user_id=".$_SESSION['user']))
            {

            }
            else
            {
                ?>
                <script>alert('There was an error while entering winners(user) ranking...');</script>
                <?php
            }
            if(mysql_query("UPDATE users SET Elo = " . $results['b'] . " WHERE user_id=".$Loser_ID))
            {

            }
            else
            {
                ?>
                <script>alert('There was an error while entering losers(opp) ranking..');</script>
                <?php
            }

        }   
        elseif($oppscore > $userscore)
        {       
            $Loser_ID = $_SESSION['user'];
            $query = mysql_query("SELECT user_id FROM users WHERE username = '".$opponent."'");
            $result = mysql_fetch_array($query) or die(mysql_error());
            $Winner_ID = $result['user_id'];

            //get rating from user table in database

            $query1 = mysql_query("SELECT Elo FROM users WHERE user_id=".$_SESSION['user']);
            $result1 = mysql_fetch_array($query1) or die(mysql_error());
            $loserRating = $result1['Elo'];

            $query2 = mysql_query("SELECT Elo FROM users WHERE user_id=".$Loser_ID);
            $result2 = mysql_fetch_array($query2) or die(mysql_error());
            $winnerRating = $result1['Elo'];

            $rating = new Rating($winnerRating, $loserRating, 1, 0);            
            $results = $rating->getNewRatings();

            $results = $rating->getNewRatings();
            if(mysql_query("UPDATE users SET Elo = " . $results['b'] . " WHERE user_id=".$_SESSION['user']))
            {

            }
            else
            {
                ?>
                <script>alert('There was an error while entering losers(user) ranking...');</script>
                <?php
            }
            if(mysql_query("UPDATE users SET Elo = " . $results['a'] . " WHERE user_id=".$Winner_ID))
            {

            }
            else
            {
                ?>
                <script>alert('There was an error while entering winners(opp) ranking...');</script>
                <?php
            }

        }
        if(mysql_query("INSERT INTO games(WinnerID,LoserID,PointsFor,PointsAgainst) VALUES('$Winner_ID','$Loser_ID','$userscore','$oppscore')"))
        {
            ?>
            <script>alert('Your scores were successfully entered');</script>
            <?php
        }
        else
        {
            ?>
            <script>alert('There was an error while entering your score...');</script>
            <?php
        }
    }
    else
    {
        ?>
        <script>alert('There cannot be a tie in ping pong, please re-enter your scores...');</script>
        <?php
    }

}
?>

Answer 1

Your query fails because it doesn't take into account the rows where the player loses. You can fix that by using unions. The following query should do what you want:

SELECT  username AS "Username",
    SUM(wins) AS "Wins",
    SUM(PF) AS "Points For",
    SUM(PA) AS "Points Against",
    elo AS "Ranking"
FROM (
    (SELECT users.user_ID,
            users.username AS username,
            COUNT(games.WinnerID) AS wins,
            SUM(games.PointsFor) AS PF,
            SUM(games.PointsAgainst) AS PA,
            users.Elo AS elo
    FROM users, games
    WHERE games.WinnerID = users.user_ID
    GROUP BY users.user_ID)
    UNION ALL
    (SELECT users.user_ID,
        users.username AS username,
        0 AS wins,
        SUM(games.PointsAgainst) AS PF,
        SUM(games.PointsFor) AS PA,
        users.Elo AS elo
    FROM users, games
    WHERE games.LoserID = users.user_ID
    GROUP BY users.user_ID)
) AS t
GROUP BY username
ORDER BY user_ID;

Note that in the "losing query" the field PointsAgainst should be counter as the player's "points for" and vice-versa.

Answer 2

Try it as an inner join, and get rid of the MIN() on the username column:

SELECT u.username, COUNT(g.WinnerID),
       SUM(g.PointsFor), SUM(g.PointsAgainst), u.Elo
  FROM users u, games g
  WHERE u.user_id = g.WinnerID
  GROUP BY u.username, u.Elo;

Also, before anyone else takes you to task, you should be using mysqli instead of mysql (or better yet, PDO) and you should be using prepared statements instead of dynamic SQL.

Answer 3

Your

INSERT INTO games(WinnerID,LoserID,PointsFor,PointsAgainst) VALUES('$Winner_ID','$Loser_ID','$userscore','$oppscore')

query contains the $userscore and $oppscore values in a potentially wrong order. The $Winner_ID and $Loser_ID may change in your conditional processing, but $userscore and $oppscore are not similarly flipped at that time.

Also your conditional structure is in general unnecessarily verbose. It seems like you should be able to just determine the winner and loser ID and score first, and then do all your processing once instead of resorting to error-prone copy-paste duplication of near-identical code.