在SQL查询中生成总计列，联接多个表

Question

I have a league system with teams, users, and then points transactions.

Each row in the points table links to a user's ID, each user row links to a team ID.

When I pull the teams from the database I want to also return a column that has the total points for that team by summing all the points associated with users in that team. I have the following code that returns the correct points total independently:

SELECT SUM(ar_points.amount) AS total_points FROM ar_teams, ar_users, ar_points WHERE ar_teams.id = ar_users.team_id AND ar_users.id = ar_points.user_id AND ar_teams.id = :id

When I pull the normal team information, it pushes the results into an object for each team:

$sql = $db->query("SELECT * FROM ar_teams");
$sql->setFetchMode(PDO::FETCH_CLASS | PDO::FETCH_PROPS_LATE,'Team');
$sql->execute();
return $sql->fetchAll();

I want to combine these two queries so that the total points value gets put into the object as another property.

Answer 1

SELECT   ar_teams.*, SUM(ar_points.amount) AS total_points
FROM     ar_teams
    JOIN ar_users  ON ar_users.team_id  = ar_teams.id
    JOIN ar_points ON ar_points.user_id = ar_users.id
GROUP BY ar_teams.id