+---------------+---------+
| Column Name | Type |
+---------------+---------+
| user1\_id | int |
| user2\_id | int |
+---------------+---------+
(user1\_id, user2\_id) is the primary key for this table.
Each row of this table indicates that the users user1\_id and user2\_id are friends.
Table: Likes
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| user\_id | int |
| page\_id | int |
+-------------+---------+
(user\_id, page\_id) is the primary key for this table.
Each row of this table indicates that user\_id likes page\_id.
You are implementing a page recommendation system for a social media website. Your system will recommended a page to user_id if the page is liked by at least one friend of user_id and is not liked by user_id.
Write an SQL query to find all the possible page recommendations for every user. Each recommendation should appear as a row in the result table with these columns:
user_id: The ID of the user that your system is making the recommendation to.
page_id: The ID of the page that will be recommended to user_id.
friends_likes: The number of the friends of user_id that like page_id.
Return result table in any order.
The query result format is in the following example:
Friendship table:
+----------+----------+
| user1\_id | user2\_id |
+----------+----------+
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 3 |
| 2 | 4 |
| 2 | 5 |
| 6 | 1 |
+----------+----------+
Likes table:
+---------+---------+
| user\_id | page\_id |
+---------+---------+
| 1 | 88 |
| 2 | 23 |
| 3 | 24 |
| 4 | 56 |
| 5 | 11 |
| 6 | 33 |
| 2 | 77 |
| 3 | 77 |
| 6 | 88 |
+---------+---------+
Result table:
+---------+---------+---------------+
| user\_id | page\_id | friends\_likes |
+---------+---------+---------------+
| 1 | 77 | 2 |
| 1 | 23 | 1 |
| 1 | 24 | 1 |
| 1 | 56 | 1 |
| 1 | 33 | 1 |
| 2 | 24 | 1 |
| 2 | 56 | 1 |
| 2 | 11 | 1 |
| 2 | 88 | 1 |
| 3 | 88 | 1 |
| 3 | 23 | 1 |
| 4 | 88 | 1 |
| 4 | 77 | 1 |
| 4 | 23 | 1 |
| 5 | 77 | 1 |
| 5 | 23 | 1 |
+---------+---------+---------------+
Take user 1 as an example:
- User 1 is friends with users 2, 3, 4, and 6.
- Recommended pages are 23 (user 2 liked it), 24 (user 3 liked it), 56 (user 3 liked it), 33 (user 6 liked it), and 77 (user 2 and user 3 liked it).
- Note that page 88 is not recommended because user 1 already liked it.
Another example is user 6:
- User 6 is friends with user 1.
- User 1 only liked page 88, but user 6 already liked it. Hence, user 6 has no recommendations.
You can recommend pages for users 2, 3, 4, and 5 using a similar process.