Optimizing SQL query with sub queries - mysql

Question

I have got a SQL query that I tried to optimize and I could reduce through various means the time from over 5 seconds to about 1.3 seconds, but no further. I was wondering if anyone would be able to suggest further improvements.
The Explain diagram shows a full scan:
explain diagram
The Explain table will give you more details:
explain tabular
The query is simplified and shown below - just for reference, I'm using MySQL 5.6
select * from (
select
#row_num := if(#yacht_id = yacht_id and #charter_type = charter_type and #start_base_id = start_base_id and #end_base_id = end_base_id, #row_num +1, 1) as row_number,
#yacht_id := yacht_id as yacht_id,
#charter_type := charter_type as charter_type,
#start_base_id := start_base_id as start_base_id,
#end_base_id := end_base_id as end_base_id,
model, offer_type, instant, rating, reviews, loa, berths, cabins, currency, list_price, list_price_per_day,
discount, client_price, client_price_per_day, days, date_from, date_to, start_base_city, end_base_city, start_base_country, end_base_country,
service_binary, product_id, ext_yacht_id, main_image_url
from (
select
offer.yacht_id, offer.charter_type, yacht.model, offer.offer_type, offer.instant, yacht.rating, yacht.reviews, yacht.loa,
yacht.berths, yacht.cabins, offer.currency, offer.list_price, offer.list_price_per_day,
offer.discount, offer.client_price, offer.client_price_per_day, offer.days, date_from, date_to,
offer.start_base_city, offer.end_base_city, offer.start_base_country, offer.end_base_country,
offer.service_binary, offer.product_id, offer.start_base_id, offer.end_base_id,
yacht.ext_yacht_id, yacht.main_image_url
from website_offer as offer
join website_yacht as yacht
on offer.yacht_id = yacht.yacht_id,
(select #yacht_id:='') as init
where date_from > CURDATE()
and date_to <= CURDATE() + INTERVAL 3 MONTH
and days = 7
order by offer.yacht_id, charter_type, start_base_id, end_base_id, list_price_per_day asc, discount desc
) as filtered_offers
) as offers
where row_number=1;
Thanks,
goppi
UPDATE
I had to abandon some performance improvements and replaced the original select with the new one. The select query is actually dynamically built by the backend based on which filter criteria are set. As such the where clause of the most inner select can expland quite a lot. However, this is the default select if no filter is set and is the version that takes significantly longer than 1 sec.
explain in text form - doesn't come out pretty as I couldn't figure out how to format a table, but here it is:
1 PRIMARY ref <auto_key0> <auto_key0> 9 const 10
2 DERIVED ALL 385967
3 DERIVED system 1 Using filesort
3 DERIVED offer ref idx_yachtid,idx_search,idx_dates idx_dates 5 const 385967 Using index condition; Using where
3 DERIVED yacht eq_ref PRIMARY,id_UNIQUE PRIMARY 4 yachtcharter.offer.yacht_id 1
4 DERIVED No tables used

Answer 1

Sub selects are never great,
You should sign up here: https://www.eversql.com/
Run that and it will give you all the right indexes and optimsiations you need for this query.

Answer 2

There's still some optimization you can use. Considering the subquery returns 5000 rows only you could use an index for it.
First rephrase the predicate as:
select *
from website_offer
where date_from >= CURDATE() + INTERVAL 1 DAY -- rephrased here
and date(date_to) <= CURDATE() + INTERVAL 3 MONTH
and days = 7
order by yacht_id, charter_type, list_price_per_day asc, discount desc
limit 5000
Then, if you add the following index the performance could improve:
create index ix1 on website_offer (days, date_from, date_to);