I know that this is a simple fix, but I can't seem to figure out how to change the code so I don't get this error:

ORA-00918: column ambiguously defined

Here is the code:

```
CREATE VIEW BOOK_INVENTORY (BRANCH_NUM, UNITS) AS    
SELECT BRANCH_NUM, ON_HAND 
FROM BRANCH, INVENTORY
WHERE BRANCH.BRANCH_NUM = INVENTORY.BRANCH_NUM
GROUP BY BRANCH.BRANCH_NUM
ORDER BY BRANCH.BRANCH_NUM;

```

Thanks in advance for the help.