Oracle/Update join

Update values in a Table using a join:

UPDATE (SELECT b.bonus, e.salary
          FROM employee_bonus b
          JOIN employees e ON b.employee_id = e.employee_id
         WHERE e.bonus_eligible = 1) t
   SET t.bonus = 0.1 * t.salary;

Views and selects with joins may only be updated when each row can be identified by a uique ID, so the join MUST be performed using key columns! In the above case, emloyee_id it the key column.

For cases where no explicit key columns exist, there are some alternatives e.g. using the MERGE statement:

MERGE INTO t_employees e
     USING (SELECT email, fist_name, last_name FROM t_user) u
        ON (u.email = e.email and u.email is not null) -- email is not a key column!
  WHEN MATCHED THEN -- update existing
    UPDATE SET e.first_name = u.first_name, e.last_name = u.last_name;