Should I be using multiple PostgreSQL queries for this? - database

Question

I have a couple of tables.
Table 1 (player_main)
This table has a "id" column which is a UUID type and is the primary key.
Table 2 (game_main)
This table also has an "id" column of the UUID type and is a primary key.
Table 3 (game_members)
This table has a column "member_id" of UUID type which is a primary key and a foreign reference to player_main(id).
There is also an "game_id" column of UUID type which references game_main(id).
My problem is, if a player connects to the server, I want to be able to load up their "game data" by querying the database and receiving all the data to construct their data object. I am given the UUID of the player which is stored in player_main(id). I need to obtain the game_main(id) and a list of all the game member ids that correspond to that game_main(id).
How would I do this? I've attempted to do different types of joins with a where clause to identify the game_members(member_id) but that only returns the row that is correspondent to the member that has just joined, not a column containing all of the members for that game.
Any help is appreciated, thank you.
Edit
I have tried the following query:
SELECT t1.member_id, t2.*
FROM game_members t1
INNER JOIN game_main t2
ON t1.game_id = t2.id
WHERE t1.member_id = <some UID>
which resulted in 1 row and 2 columns. The columns being "game_members.member_id" and "game_main.id". The value for the first column is the UUID that I specified in the where clause and the value for the second column is the UUID of the game. I was expecting to see 2 rows of data with the same "game_main.id" but with different "game_member.member_id"'s, as I have 2 entries in the same game currently.
Edit 2
As requested, I will provide sample data for my tables as well as the output that I wish to see.
Sample Data:
[player_main]
id
------------------------------------|
863fdf91-86fb-49a7-9232-bcb596e3a86f|
7af64cd7-72a2-410f-9b5c-620127fca0ac|
c7b1952a-b263-470f-9cae-9d5e6d7a8186|
[game_main]
id
------------------------------------|
dd76c680-5853-40a6-b757-0457d1a7e95f|
ca4f5b1f-0f8c-4f10-969c-464ccf207d9c|
[game_members]
member_id | game_id
------------------------------------|------------------------------------
863fdf91-86fb-49a7-9232-bcb596e3a86f|dd76c680-5853-40a6-b757-0457d1a7e95f
7af64cd7-72a2-410f-9b5c-620127fca0ac|dd76c680-5853-40a6-b757-0457d1a7e95f
c7b1952a-b263-470f-9cae-9d5e6d7a8186|ca4f5b1f-0f8c-4f10-969c-464ccf207d9c
[desired output]
This is what the game info of the player's current game should look like. The query should take only the player's UUID and return the following if I the UUID was equal to 863fdf91-86fb-49a7-9232-bcb596e3a86f
member_id | game_id
------------------------------------|------------------------------------
863fdf91-86fb-49a7-9232-bcb596e3a86f|dd76c680-5853-40a6-b757-0457d1a7e95f
7af64cd7-72a2-410f-9b5c-620127fca0ac|dd76c680-5853-40a6-b757-0457d1a7e95f

Answer 1

Try doing a self-join of the game_members table. The following query will generate all unique members who have any game in common with games used by a certain player.
SELECT DISTINCT t2.member_id, t1.game_id
FROM game_members t1
INNER JOIN game_members t2
ON t1.game_id = t2.game_id
WHERE t1.member_id = <some UID>

Answer 2

You could break down your problem into:
looking up the player's current game in game_members and then,
looking up the game's current players from the same game_members table
This approach translates to the following query involving a self-join:
select
gm2.member_id,
gm1.game_id
from
game_members gm1
inner join game_members gm2 on
gm1.game_id = gm2.game_id -- lookup the game's current players
where
gm1.member_id = '863fdf91-86fb-49a7-9232-bcb596e3a86f' -- lookup the player's current game