Query 1 AFTER:
A)
PROFILE:

mysql> show profile for query 112;
+--------------------+----------+
| Status             | Duration |
+--------------------+----------+
| starting           | 0.000084 |
| Opening tables     | 0.000016 |
| System lock        | 0.000005 |
| Table lock         | 0.000009 |
| init               | 0.000026 |
| optimizing         | 0.000011 |
| statistics         | 0.000030 |
| preparing          | 0.000014 |
| executing          | 0.000003 |
| Sending data       | 0.180282 |
| end                | 0.000016 |
| query end          | 0.000004 |
| freeing items      | 0.001778 |
| logging slow query | 0.000006 |
| cleaning up        | 0.000006 |
+--------------------+----------+
15 rows in set (0.00 sec)

EXPLAIN:

mysql> EXPLAIN SELECT SQL_NO_CACHE c.owner,p.time FROM car c, passing p
    -> WHERE p.regno=c.regno;
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref        | rows   | Extra       |
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------------+
|  1 | SIMPLE      | p     | index  | PRIMARY       | PRIMARY | 32      | NULL       | 100000 | Using index |
|  1 | SIMPLE      | c     | eq_ref | PRIMARY       | PRIMARY | 10      | db.p.regno |      1 |             |
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------------+
2 rows in set (0.00 sec)


B)



C)
Profile:

mysql> show profile for query 142;
+--------------------+----------+
| Status             | Duration |
+--------------------+----------+
| starting           | 0.000106 |
| Opening tables     | 0.000017 |
| System lock        | 0.000005 |
| Table lock         | 0.000009 |
| init               | 0.000028 |
| optimizing         | 0.000012 |
| statistics         | 0.000026 |
| preparing          | 0.000014 |
| executing          | 0.000003 |
| Sending data       | 0.893014 |
| end                | 0.000022 |
| query end          | 0.000003 |
| freeing items      | 0.001403 |
| logging slow query | 0.000003 |
| cleaning up        | 0.000187 |
+--------------------+----------+
15 rows in set (0.00 sec)


Explain:

mysql> EXPLAIN SELECT c.owner, p.time FROM car c FORCE INDEX(PRIMARY), passing p IGNORE INDEX(PRIMARY) WHERE p.regno=c.regno;
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref        | rows   | Extra |
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------+
|  1 | SIMPLE      | p     | ALL    | NULL          | NULL    | NULL    | NULL       | 100000 |       |
|  1 | SIMPLE      | c     | eq_ref | PRIMARY       | PRIMARY | 10      | db.p.regno |      1 |       |
+----+-------------+-------+--------+---------------+---------+---------+------------+--------+-------+
2 rows in set (0.00 sec)