我怎样才能用 SQL 实现这一点？

Question

Let's say i have a single table called mytable with the following data :

https://i.stack.imgur.com/hvLHO.png

i'm interested in having IDs who belong to both categories A and B

The desired result would be like this :

https://i.stack.imgur.com/nPmW1.png

i tried :

select * from mytable where category in ('A','B');

but it doesn't seem to work

Answer 1

You can use exists :

select t.*
from mytable t
where 
    category in ('A', 'B')
    and exists (
        select 1 
        from mytable t1 
        where t1.id = t.id and t1.category in ('A', 'B') and t1.category <> t.category
    )

Another approach is a window count (assuming no duplicate in (id, category) tuples):

select id, price, category
from (
    select t.*, count(*) over(partition by id) cnt
    from mytable t
    where category in ('A', 'B')
) t
where cnt > 1