Preventing duplicate values in multiple joins of the same table - ruby-on-rails

Question

I have two tables in my project that I need to join together in a somewhat complicated way and it is giving me very strange issues
I have a concept of teams and a concept of FeedItems. FeedItems means the team has solved a challenge. I need to know the last time they solved a challenge at, and I also need to calculate the sum of point-based FeedItems.
SELECT COALESCE(sum(challenges.point_value), 0) + COALESCE(sum(point_feed_items.point_value), 0) as team_score,
GREATEST(MAX(pentest_feed_items.created_at), MAX(point_feed_items.created_at)) as last_solve_time, teams.* FROM "teams"
LEFT JOIN feed_items AS point_feed_items
ON point_feed_items.team_id = teams.id
AND point_feed_items.type IN ('StandardSolvedChallenge', 'ScoreAdjustment')
LEFT JOIN feed_items AS pentest_feed_items
ON pentest_feed_items.team_id = teams.id
AND pentest_feed_items.type IN ('PentestSolvedChallenge')
LEFT JOIN challenges ON challenges.id = point_feed_items.challenge_id
AND challenges.type IN ('StandardChallenge') WHERE "teams"."division_id" = $1
GROUP BY teams.id ORDER BY "teams"."created_at" ASC
This works nearly all the time, I am just running into an edge case where I will sometimes end up with the same ScoreAdjustment in the point_feed_items.point_value sum. I called COUNT(point_feed_items.point_value) and verified that I somehow had 3 elements coming back even though there should only be 1. I have so far been unable to figure out either why the same element is sometimes coming back multiple times, or how to call DISTINCT as part of the LEFT JOIN to avoid the problem completely.
I did find that removing the 2nd LEFT JOIN did fix the issue, however I need the data from that LEFT JOIN.
To put the issue another way, I replaced COALESCE(sum(point_feed_items.point_value), 0) with COALESCE(COUNT(point_feed_items.point_value), 0) and verified with no ScoreAdjustments in the database that it returned 0. I then created one ScoreAdjustment with the correct team and COALESCE(COUNT(point_feed_items.point_value), 0) then returned 3 instead of 1. Am I misunderstanding how LEFT JOIN AS works?
This is part of a rails app, however it is mostly written as a manual query for better performance.

Answer 1

Turns out this was all due to a misunderstanding of how LEFT JOIN works when you do it multiple times.
Given the following (simplified example) data:
I was thinking of the LEFT JOIN as looking something like this:
And it actually looked something like this:
I went ahead and switched my query over to look as follows:
SELECT COALESCE(sum(point_feed_items.team_score), 0) as team_score,
GREATEST(MAX(pentest_feed_items.last_solve_time),
MAX(point_feed_items.last_solve_time)) as last_solve_time,
teams.*
FROM "teams"
LEFT JOIN LATERAL
(
SELECT
COALESCE(sum(challenges.point_value), 0) + COALESCE(sum(feed_items.point_value), 0) as team_score,
MAX(feed_items.created_at) as last_solve_time
FROM feed_items
LEFT JOIN challenges ON challenges.id = feed_items.challenge_id AND challenges.type IN ('StandardChallenge')
WHERE feed_items.team_id = teams.id
AND feed_items.type IN ('StandardSolvedChallenge', 'ScoreAdjustment')
) AS point_feed_items ON true
LEFT JOIN LATERAL
(
SELECT MAX(feed_items.created_at) as last_solve_time
FROM feed_items
WHERE feed_items.team_id = teams.id
AND feed_items.type IN ('PentestSolvedChallenge')
) AS pentest_feed_items ON true
WHERE "teams"."division_id" = $1 GROUP BY teams.id
And everything works fine now.