Restock Gap Tracker :Calculate the Gap Between Restock Events Intermediate

          select productid,
       inventoryid,
       lastrestocked::date as restock_date,
       lag(lastrestocked::date) over (partition by productid
                                      order by lastrestocked::date) as previous_restock_date,
                                     lastrestocked::date - lag(lastrestocked::date) over (partition by productid
                                                                                          order by lastrestocked::date) as days_between_restocks
from inventory
order by productid,
         restock_date;