SQL中如何查询这个结果？ 或者也许在 python？

Question

I have a table with multiple user_id and each one can redeem a discount code like this:

user_id	discount_code
1	A
2	B
3	A
1	B
2	A
1	A
1	B
2	A
2	B
3	A

I have to count the overlap of users for each discount code.

I think this should be the result:

	A	B
A	3	2
B	2	2

Answer 1

Consider below approach

select * from (
  select t1.discount_code, t2.discount_code code, count(distinct t1.user_id) value
  from your_table t1
  join your_table t2
  using(user_id)
  group by 1, 2
)
pivot (any_value(value) for code in ('A', 'B'))    

if applied to sample data in your question - output is