The following thread successfully showed how to use a an UPDATE SET and FROM clause together, to update an entire row of a specific column with a value derived from a different table.
When executing following expression in Oracle SQL:
UPDATE territory2_t
SET total_sales_person = t.total_count
FROM (
SELECT salesterritoryid, count(*) as total_count
FROM salesperson_t
group by salesterritoryid
) t
WHERE territoryid = t.salesterritoryid;
Oracle states: SQL Error: ORA-00933: SQL command not properly ended