如何在django中更新id表单

Question

如何更新Django中的id字段，例如我有：

mysql> SELECT * FROM school_subjects;
+----+--------+---------+-------------+
| id | name   | user_id | delete_flag |
+----+--------+---------+-------------+
|  1 | Canada |       2 |           0 |
|  2 | USA    |       2 |           0 |
+----+--------+---------+-------------+

如果我删除它们，然后再次更新，我的ID将继续递增：

mysql> SELECT * FROM school_subjects;
+----+--------+---------+-------------+
| id | name   | user_id | delete_flag |
+----+--------+---------+-------------+
|  3 | Canada |       2 |           0 |
|  4 | USA    |       2 |           0 |
+----+--------+---------+-------------

+ 那么如何让id字段检查最低的字段，然后从那里增加它？

#models.py
class Subjects(models.Model):
    """ Subject Database """
    name = models.CharField(max_length=64, unique=False) #Subject Names on left-menu 
    user = models.ForeignKey(User, unique=False)
    delete_flag = models.BooleanField(default=False)

    def __unicode__(self):
        return '%s %s' %(self.name, self.user.username)