Sql query performance is varying though they are the same - mysql

Question

There are 2 tables and their structure as below:
mysql> desc product;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| brand | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.02 sec)
mysql> desc sales;
+-------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| yearofsales | varchar(10) | YES | | NULL | |
| price | int(11) | YES | | NULL | |
+-------------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
Here id is the foreign key.
And Queries are as follows:
1.
mysql> select brand,sum(price),yearofsales
from product p, sales s
where p.id=s.id
group by s.id,yearofsales;
+-------+------------+-------------+
| brand | sum(price) | yearofsales |
+-------+------------+-------------+
| Nike | 917504000 | 2012 |
| FF | 328990720 | 2010 |
| FF | 328990720 | 2011 |
| FF | 723517440 | 2012 |
+-------+------------+-------------+
4 rows in set (1.91 sec)
2.
mysql> select brand,tmp.yearofsales,tmp.sum
from product p
join (
select id,yearofsales,sum(price) as sum
from sales
group by yearofsales,id
) tmp on p.id=tmp.id ;
+-------+-------------+-----------+
| brand | yearofsales | sum |
+-------+-------------+-----------+
| Nike | 2012 | 917504000 |
| FF | 2011 | 328990720 |
| FF | 2012 | 723517440 |
| FF | 2010 | 328990720 |
+-------+-------------+-----------+
4 rows in set (1.59 sec)
Question is: Why the second query takes less time than the first one? I have executed it multiple times in different order as well.

Answer 1

You can check the execution plan for the two queries and the indexes on the two tables to see why one query takes more than the other. Also, you cannot run one simple test and trust the results, there are many factors that can impact the execution of queries, like the server being busy with something else when executing one query, so it runs slower. You'll have to run both queries a big number of times and then compare the averages.
However, it is highly recommended to use explicit joins instead of implicit joins:
SELECT brand, SUM(price), yearofsales
FROM product p
INNER JOIN sales s ON p.id = s.id
GROUP BY s.id, yearofsales;