Any idea why I'm receiving the invalid identifier error? It's my first time using Over(Partition by

SELECT
a.day AS date
b.location AS region,
c.item AS product,
d.details AS description,
SUM(a.hours) over(partition BY a.day, b.location, c.item, d.details) AS item_hours,
SUM(a.hours) over(partition BY a.day, b.location, d.details) AS hours,
FROM Time_data a,
Geography_data b,
Items_data c,
Description_data d
WHERE a.code = b.code
AND a.code = c.code
AND a.code = d.code


Error report:
SQL Error: ORA-00904: "C"."item": invalid identifier

SUM(a.hours) over(partition BY a.day, b.location, d.details) AS hours,
FROM Time_data a,