SQL、label用户基于相似度

Question

Is below case possible in SQL?

Let say I have a table like this:

user_id	product_id
1	123
1	122
1	121
2	124
2	125
2	121
3	123
3	122
3	122
4	123
4	212
4	222
5	124
5	125
5	121

I want to label the user if they have same product_id, regardless the order, so the output looks like this:

user_id	product_id	label
1	123	a
1	122	a
1	121	a
2	124	b
2	125	b
2	121	b
3	123	a
3	121	a
3	122	a
4	123	c
4	212	c
4	222	c
5	124	b
5	125	b
5	121	b

Please advise

Answer 1

You can use the string_agg function to get the list of product_ids for each user (as a single string), then use the dense_rank function on that string to get unique labels for each product_ids list.

select T.user_id, T.product_id, D.label
from table_name T join
(
  select user_id, 
    chr(dense_rank() over (order by user_products) + 96) label
  from
  (  
   select user_id, 
    string_agg(cast(product_id as string), ',' order by product_id)  user_products
   from table_name
   group by user_id
  ) lbl
) D
on T.user_id = D.user_id
order by T.user_id