Select records from table A that have at least X records on table B

Question

I have a table called users another table called user_flags , and another table called flags

The users table contains a name and id

The flags table contains a name and id

The user_flags contains a user_id and flag_id

If I want to get all the users which have any of the provided flag names, what would be the query? That is, if the query provides 'red' and 'blue' but a user is just associated with blue, we would return that User.

That is, if I have the following schema: http://sqlfiddle.com/#!9/ac105 - And the flag names that I passed were red and blue , it would return the row for the User John, because John has a red associated flag.

Answer 1

Try this query:

SELECT u.name
FROM users u INNER JOIN user_flags uf
ON u.id = uf.user_id
INNER JOIN flags f
ON uf.flag_id = f.id
WHERE F.name = 'red'

SQL Fiddle

Note that in the fiddle the table and column names are slightly different from what you used in your original question.

Answer 2

You need to join the tables on their id values and use a where clause for the flag color name. Something like this:

select * from Users U
  join UsersFlags UF on UF.user_id = U.id
  join Flags F on F.id = UF.flag_id
  where F.name = 'red'

Answer 3

Try this one

SELECT s.id,s.name 
FROM @users s 
JOIN @users_flag uf ON s.id = uf.uid
JOIN @flag f ON f.id = uf.fid
WHERE f.NAME IN ('red','Blue')

Answer 4

SELECT u.id
      ,u.name
      ,f.name flag 
FROM USERS u
     JOIN flags f using(id)
     JOIN UsersFlags uf on f.id=uf.flag_id
WHERE
f.name in ('red','blue') -- or f.name in (select name from flags)
                         -- or f.name = any(array['red','blue'])

and another one

SELECT u.NAME
FROM USERS u
WHERE id IN (
        SELECT uf.user_id
        FROM UsersFlags uf
        JOIN flags f ON uf.flag_id = f.id
        WHERE f.NAME IN (
                'red'
                ,'blue'
                )
        )

output:

id name flag 
-- ---- ---- 
1  John red