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Exercise 23:1892.Page Recommendations II

1.Description

Table: Friendship
+---------------+---------+
| 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 recommend 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.

2.Create Table and insert into values

create table if not exists leetcode.ex_1892_friendship
(user1_id string , user2_id string ) stored as orc ;
​
INSERT INTO table leetcode.ex_1892_friendship VALUES
('1','2'),
('1','3'),
('1','4'),
('2','3'),
('2','4'),
('2','5'),
('6','1') ;
​
create table if not exists leetcode.ex_1892_likes
(user_id string , page_id string ) stored as orc ;
​
INSERT INTO table leetcode.ex_1892_likes VALUES
('1','88'),
('2','23'),
('3','24'),
('4','56'),
('5','11'),
('6','33'),
('2','77'),
('3','77'),
('6','88') ;
User 1 is friends with users 2, 3, 4, and 6:
user1_id = 1,user2_id =(2,3,4) and user2_id=1, user1_id =6 , it means for user1, he's friend =(2,3,4,6).
SO the first step, we have to do data processing on Friendship table.
​