Question

TABLE users_community_relations

list_id int user_id int dest_user_id int
  1           10            20
  2           10            24
  3           10            33
  4           11            10

TABLE users_avatar

avatar_id int user_id int  webavatar_thumbnail
    1            10            test.jpg
    2            10            test2.jpg
    3            20            test2.jpg
    4            20            test11.jpg

TABLE users

user_id int  nick varchar
  10         kaka
  20         caca
  24         dada
  33         roro

I need to query this three tables there is the logic, table users_community_relations wheen i put user_id = 10 for example i get results from same table column dest_user_id 20,24,33 each number represent user_id in next two tables, i would need to get all data from next two tables accordingly to 20,24,33 numbers from dest_user_id column. Sometimes table users_avatar does not hold any avatar for user in that case string from this table could be empty. Sometimes it holds more than two rows, in that case i would need to get only first one but ordered with avatar_id DESC users_avatar table.

Answer 1

This should work:

SELECT ucr.*, u.*, ua1.*
FROM users_community_relations ucr
LEFT JOIN users u
  ON u.user_id = ucr.user_id
LEFT JOIN users_avatar ua1
  ON ua1.user_id = u.user_id
LEFT JOIN users_avatar ua2
  ON ua2.user_id = u.user_id AND ua2.avatar_id > ua1.avatar_id
WHERE ua2.avatar_id IS NULL

It uses joins to ensure we only return the user_avatar row with the highest avatar_id or NULL if there is no avatar.