子查询：根据匹配的用户ID和团队ID从一张表中进行选择，并输出二维数组

Question

I want to select from login_users to get the following fields: name , username , and user_id .

I have a separate table teams with the team_id, as well as the associated user_id , so for example I might have bob with team1, jack with team2, jim with team1, and paul with team2 (all separate rows, not bob and paul -> team2). If I provide a function with the team_ id I want to be able to find all the associated user_id s, and then match that data with login_users to output a two dimensional array that has name , username , and user_id of all the team members.

SELECT username, user_id, name FROM login_users WHERE EXISTS ( SELECT user_id FROM teams WHERE team_id= $team_id );

I know it has something to do with sub queries I just have never done them before, and I feel that I am on the wrong track. Furthermore, how would I then go about producing a two dimensional array?

Answer 1

Why only subquery ?? why not JOIN

SELECT u.username, u.user_id, u.`name` FROM login_users u
JOIN teams t ON(u.user_id = t.user_id)
WHERE team_id= $team_id 

Answer 2

If you want to do this with an "exists" subquery, then it needs to be a correlated subquery:

SELECT username, user_id, name
FROM login_users
WHERE EXISTS (SELECT user_id
              FROM teams
              WHERE team_id = $team_id and
                    teams.user_id = login_users.team_id
             );

You are missing the condition on the user_id . That version of the query is saying "get me all rows from login_users when team_id exists in teams ".