脸书非常中规中矩的店面跪经

写的一些sql：

1. select user_id, date
   
2. from
   
3. (select user_id, date, rank() over(partition by user_id order by date) as rk
   
4. from user_log
   
5. where user_action = 'login')
   
6. where rk = 1;
   
7. 
   
8. 
   
9. 
   
10. select user1, count(distinct user2) as num_friend
    
11. from
    
12. (select user1， user2
    
13. from friend
    
14. where friend_request = 'approved'
    
15. union all
    
16. select user2 as user1, user1 as user2
    
17. from friend
    
18. where friend_request = 'approved')
    
19. group by user1
    
20. order by num_friend desc
    
21. limit 3;
    
22. 
    

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