SQL - Check if an item was available in the previous month and then flag it

Question

I'm trying to solve a problem in SQL but without much success so far. I have a table like this:

OWNER|STORE|DATE
  A  | MIX |01/01/2019
  A  | BIX |01/01/2019
  A  | BIX |02/01/2019
  B  | CIX |01/01/2019
  B  | CIX |02/01/2019

It's a table showing information about owners and their stores. An owner can have a store during a month, but this store could be gone in the next month. Or, their store could be present in january, but gone in february.

I wanted to find a way to flag this store movement, so if a store is present in january, and gone in february, I would flag a colum as "gone". And if a store was not present in january, but appeared in february, I would flag it as "new".

Can anyone help me with that? Thanks!

Answer 1

select d.store ,d.owner , d.timedate , 'new' flag from (
  SELECT
 a.store, count(a.store) as flag
FROM
  store as a
  left join  store as b
  on a.store=b.store
group by a.store
having(count(a.store)<2)) as c

  inner join store as d
  on c.store=d.store

union all
(SELECT
 a.store , a.owner, max(a.timedate ), 'gone' as [flag]
FROM
  store as a
  inner  join
  (SELECT
 owner,store,timedate

FROM store) as b
on b.store = a.store and a.timedate!=b.timedate
group by a.store , a.owner)

sqlfiddle here