MySQL query optimization, VERY SLOW - mysql

Question

This is what I would like to achieve:
Show 50 last students and their cheapest products.
If product doesn't exist present empty values.
Here is the SELECT query:
SELECT
students.*,
cs.cheapest_id,
cs.cheapest_price
FROM students
LEFT JOIN (SELECT iqs.* FROM (
SELECT
student_id,
id AS cheapest_id,
price AS cheapest_price
FROM products
ORDER BY price ASC
) AS iqs
GROUP BY iqs.student_id) AS cs ON cs.student_id = students.id
ORDER BY students.name DESC
LIMIT 50;
Creating tables:
CREATE TABLE `students` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
INSERT INTO `students` VALUES ('1', 'Mark');
INSERT INTO `students` VALUES ('2', 'Chris');
CREATE TABLE `products` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`student_id` int(11) DEFAULT NULL,
`price` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `student_id` (`student_id`)
) ENGINE=MyISAM AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
INSERT INTO `products` VALUES ('1', '1', '2');
INSERT INTO `products` VALUES ('2', '1', '3');
Result:
id name cheapest_id cheapest_price
1 Mark 1 2
2 Chris (NULL) (NULL)
Here is the problem:
If there are many records in both tables query is very slow(minutes).
If I use INNER JOIN instead of LEFT JOIN or if I remove "ORDER BY students.name DESC" query is fast.
I have set index on student_id but still it is very slow.
Can anyone please help? I've been struggling with this for days...
Edit: The result of EXPLAIN
1 PRIMARY students ALL 3 Using temporary; Using filesort
1 PRIMARY <derived2> ALL 2
2 DERIVED <derived3> ALL 4 Using temporary; Using filesort
3 DERIVED products ALL 4 Using filesort

Answer 1

Try adding these indexes:
ALTER TABLE `students` ADD INDEX (`id`, `name`);
ALTER TABLE `products` ADD INDEX (`student_id`, `id`, `price`);
and write your query like this:
SELECT students.*,
MIN(products.id) AS cheapest_id,
MIN(products.price) AS cheapest_price
FROM students
LEFT JOIN products ON student_id = students.id
GROUP BY students.id
ORDER BY students.name DESC
LIMIT 50;
You should definately read about the EXPLAIN SELECT syntax and how to index properly:
https://dev.mysql.com/doc/refman/5.6/en/explain.html
https://dev.mysql.com/doc/refman/5.5/en/optimization-indexes.html
With EXPLAIN SELET %YOUR QUERY% you can see how MySQL is optimizing the query and how the engine is actually reading your datasets.