how to output a standings table on the fly from a mysql table of football [soccer] results?

First union the scores table together swapping the hometeam with the awayteam and swapping the goal counts. This gives you some source data that is easily aggregated and the query to generate the score card is something like this:

select 
    team, 
    count(*) played, 
    count(case when goalsfor > goalsagainst then 1 end) wins, 
    count(case when goalsagainst> goalsfor then 1 end) lost, 
    count(case when goalsfor = goalsagainst then 1 end) draws, 
    sum(goalsfor) goalsfor, 
    sum(goalsagainst) goalsagainst, 
    sum(goalsfor) - sum(goalsagainst) goal_diff,
    sum(
          case when goalsfor > goalsagainst then 3 else 0 end 
        + case when goalsfor = goalsagainst then 1 else 0 end
    ) score 
from (
    select hometeam team, goalsfor, goalsagainst from scores 
  union all
    select awayteam, goalsagainst, goalsfor from scores
) a 
group by team
order by score desc, goal_diff desc;

// connection stuff
$sql = 'select * from matchesTable';
$result = mysql_query($sql)

$standings = array ();
$standingTemplate = array ('matches' => 0, 'wins' => 0, 'draws' => 0, 'losses' => 0, 'goalsfor' => 0, 'goalsagainst' => 0, 'goalsdiff' => 0, 'points' => 0);

while ($row = mysql_fetch_assoc($result)) 
{
    handleMatch($row['hometeam'], $row['goalsfor'], $row['goalsagainst']);
    handleMatch($row['awayteam'], $row['goalsfor'], $row['goalsagainst']);

    print_r( usort(standings, 'comparePoints') );  // up to you to format the output as you like
}

function handleMatch($team, $goalsfor, $goalsagainst)
{
    global $standings, $standingTemplate;
    if ($goalsfor > $goalsagainst) 
    {
        $points = 3;
        $win = 1;
        $draw = 0;
        $loss = 0;
    }
    elsif ($goalsfor == $goalsagainst) 
    {
        $points = 1;
        $win = 0;
        $draw = 1;
        $loss = 0;
    }
    else 
    {
        $points = 0
        $win = 0;
        $draw = 0;
        $loss = 1;
    }

    if ( empty($standings[$team]) )$standing = $standingTemplate;
    else $standing = $standings[$team];

    $standing['matches']++;
    $standing['wins'] += $win;
    $standing['draws'] += $draw;
    $standing['losses'] += $loss;
    $standing['goalsfor'] += $goalsfor;
    $standing['goalsagainst'] += $goalsagainst;
    $standing['goalsdiff'] += $goalsfor - $goalsagainst;
    $standing['points'] += $points;

    $standings[$team] = $standing;

}

function comparePoints($a, $b)
{
    if ($a['points'] == $b['points']) 
    {
        if ($a['goalsdiff'] == $b['goalsdiff']) return 0;
        return ($a['goalsdiff'] < $b['goalsdiff']) ? 1 : -1 ;
    }       
    return ($a['points'] < $b['points']) ? 1 : -1 ;
}

NOTES: I didn't test it and all, might be little bug (some $ or ; missing).

Recently I had to make quite more extended version of datatable. Although it is based on my own schema, but it maybe useful for someone (it is based on previous a'r answer):

  SELECT
    team_id                                             team_id,
    t.name                                              team_name,
    t.country                                           country,
    count(*)                                            matches,
    SUM(scored)                                         scored_total,
    SUM(conceided)                                      conceided_total,
    count(CASE WHEN scored > conceided
      THEN 1 END)                                       wins,
    count(CASE WHEN scored = conceided
      THEN 1 END)                                       draws,
    count(CASE WHEN scored < conceided
      THEN 1 END)                                       lost,
    sum(scored) - sum(conceided)                        balance,
    sum(
        CASE WHEN scored > conceided
          THEN 3
        ELSE 0 END
        + CASE WHEN scored = conceided
          THEN 1
          ELSE 0 END)                                   points,
    count(CASE WHEN place = 'home'
      THEN 1 END)                                       home_matches,
    count(CASE WHEN place = 'home' AND scored > conceided
      THEN 1 END)                                       home_wins,
    count(CASE WHEN place = 'home' AND scored = conceided
      THEN 1 END)                                       home_draws,
    count(CASE WHEN place = 'home' AND scored < conceided
      THEN 1 END)                                       home_lost,
    SUM(CASE WHEN place = 'home'
      THEN scored
        ELSE 0 END)                                     home_scored,
    SUM(CASE WHEN place = 'home'
      THEN conceided
        ELSE 0 END)                                     home_conceided,
    count(CASE WHEN place = 'away'
      THEN 1 END)                                       away_matches,
    count(CASE WHEN place = 'away' AND scored > conceided
      THEN 1 END)                                       away_wins,
    count(CASE WHEN place = 'away' AND scored = conceided
      THEN 1 END)                                       away_draws,
    count(CASE WHEN place = 'away' AND scored < conceided
      THEN 1 END)                                       away_lost,
    SUM(CASE WHEN place = 'away'
      THEN scored
        ELSE 0 END)                                     away_scored,
    SUM(CASE WHEN place = 'away'
      THEN conceided
        ELSE 0 END)                                     away_conceided,
    GROUP_CONCAT((CASE
                  WHEN scored > conceided
                    THEN 'W'
                  WHEN scored = conceided
                    THEN 'D'
                  WHEN scored < conceided
                    THEN 'L'
                  END) ORDER BY date ASC separator '') streak
  FROM
    (
      (SELECT
         hm.date         date,
         hm.home_team_id team_id,
         hm.score_home   scored,
         hm.score_away   conceided,
         'home'          place
       FROM matches hm
       WHERE hm.season_id = :seasonId)
      UNION ALL
      (SELECT
         am.date         date,
         am.away_team_id team_id,
         am.score_away   scored,
         am.score_home   conceided,
         'away'          place
       FROM matches am
       WHERE am.season_id = :seasonId)
    ) m
    JOIN teams t ON t.id = team_id
  GROUP BY team_id
  ORDER BY points DESC, balance DESC;