Optimize mysql query with subqueries - mysql

Question

Below is MySQl query with which I am able to get disired result
But is there any way i could optimize the query
SELECT users.*,
(SELECT country_name FROM country WHERE country_code = users.country_code)
AS country_name,
(SELECT zone_name FROM timezone WHERE timezone_id = users.timezone_id)
AS zone_name,
(SELECT GROUP_CONCAT(list_name)
FROM list LEFT JOIN user_list ON user_list.list_id = list.list_id
WHERE user_list.user_id = users.user_id AND user_list.status = "active")
AS groups,
(SELECT GROUP_CONCAT(promotion_name)
FROM promotion LEFT JOIN promotion_user ON promotion_user.promotion_id = promotion.promotion_id
WHERE promotion_user.user_id = users.user_id AND promotion_user.status = "active")
AS promotions,
(SELECT GROUP_CONCAT(full_name)
FROM users u LEFT JOIN promotion_user ON promotion_user.promotor_id = u.user_id
WHERE promotion_user.user_id = users.user_id AND promotion_user.status = "active")
AS promotors
FROM users WHERE client_id = '2' AND status != 'deleted'
ORDER BY user_id desc
LIMIT 50 OFFSET 0
The Explain Output is
possible key
id select_type table type _keys key _len ref rows Extra
1 PRIMARY users index NULL PRIMARY 4 NULL 1045612 Using where
6 DEPENDENT SUBQUERY promotion_user ALL NULL NULL NULL NULL 16159 Using where
6 DEPENDENT SUBQUERY u eq_ref PRIMARY PRIMARY 4 [1] 1 NULL
5 DEPENDENT SUBQUERY promotion_user ALL NULL NULL NULL NULL 16895 Using where
5 DEPENDENT SUBQUERY promotion ALL PRIMARY NULL NULL NULL 4 Using where; Using join buffer (Block Nested Loop)
4 DEPENDENT SUBQUERY list ALL PRIMARY NULL NULL NULL 1592 NULL
4 DEPENDENT SUBQUERY user_list ALL NULL NULL NULL NULL 159852 Using where; Using join buffer (Block Nested Loop)
3 DEPENDENT SUBQUERY timezone eq_ref PRIMARY PRIMARY 4 [2] 1 NULL
2 DEPENDENT SUBQUERY country ALL NULL NULL NULL NULL 239 Using where
[1] test.promotion_user.promoter_id
[2] test.promotion_user.promoter_id

Answer 1

I would try using non correlated sub queries. However as you are only bringing back the details for a single user (hence a single row probably) this might not help. Beyond probably eliminating one sub query.
Something like this (untested as no data definitions or data examples)
SELECT `users`.*,
country.country_name,
timezone.zone_name,
sub_groups.groups,
sub_promotors.promotions,
sub_promotors.promotors
FROM `users`
INNER JOIN country
ON country.country_code = users.country_code
INNER JOIN timezone
ON timezone.timezone_id = users.timezone_id
INNER JOIN
(
SELECT promotion_user.user_id, GROUP_CONCAT(full_name) AS promotors, GROUP_CONCAT(promotion_name) AS promotions
FROM users u
LEFT JOIN promotion_user ON promotion_user.promotor_id = u.user_id
WHERE promotion_user.status = "active"
GROUP BY promotion_user.user_id
) AS sub_promotors
ON sub_promotors.user_id = users.user_id
INNER JOIN
(
SELECT user_list.user_id, GROUP_CONCAT(list_name) AS groups
FROM list
LEFT JOIN user_list ON user_list.list_id = list.list_id
WHERE user_list.status = "active"
GROUP BY user_list.user_id
) AS sub_groups
ON sub_groups.user_id = users.user_id
WHERE users.client_id = '2'
AND users.status != 'deleted'
ORDER BY users.user_id
DESC LIMIT 50 OFFSET 0
Correlated sub queries effectively forces MySQL to perform themselves once for each returned row. Changing these to non correlated sub queries which are joined means they can be performed once for all returned rows. Down side is that joining onto a sub query is poorly optimised as far as indexes in MySQL.
You might be able to remove the sub queries if the promotor full name, etc are unique.