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  • MySQL multiple dependent subqueries, painfully slow

    - by matt80
    I have a working query that retrieves the data that I need, but unfortunately it is painfully slow (runs over 3 minutes). I have indexes in place, but I think the problem is the multiple dependent subqueries. I've been trying to rewrite the query using joins but I can't seem to get it to work. Any help would be greatly appreciated. The tables: Basically, I have 2 tables. The first (prices) holds the prices of items in a store. Each row is the price of an item that day, and new rows are added every day with an updated price. The second table (watches_US) holds the item information (name, description, etc). CREATE TABLE `prices` ( `prices_id` int(11) NOT NULL auto_increment, `prices_locale` enum('CA','DE','FR','JP','UK','US') NOT NULL default 'US', `prices_watches_ID` char(10) NOT NULL, `prices_date` datetime NOT NULL, `prices_am` varchar(10) default NULL, `prices_new` varchar(10) default NULL, `prices_used` varchar(10) default NULL, PRIMARY KEY (`prices_id`), KEY `prices_am` (`prices_am`), KEY `prices_locale` (`prices_locale`), KEY `prices_watches_ID` (`prices_watches_ID`), KEY `prices_date` (`prices_date`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=61764 ; CREATE TABLE `watches_US` ( `watches_ID` char(10) NOT NULL, `watches_date_added` datetime NOT NULL, `watches_last_update` datetime default NULL, `watches_title` varchar(255) default NULL, `watches_small_image_height` int(11) default NULL, `watches_small_image_width` int(11) default NULL, `watches_description` text, PRIMARY KEY (`watches_ID`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; The query retrieves the last 10 prices changes over a period of 30 hours, ordered by the size of the price change. So I have subqueries to get the newest price, the oldest price within 30 hours, and then to calculate the price change. Here's the query: SELECT watches_US.*, prices.*, watches_US.watches_ID as current_ID, ( SELECT prices_am FROM prices WHERE prices_watches_ID = current_ID AND prices_locale = 'US' ORDER BY prices_date DESC LIMIT 1 ) as new_price, ( SELECT prices_date FROM prices WHERE prices_watches_ID = current_ID AND prices_locale = 'US' ORDER BY prices_date DESC LIMIT 1 ) as new_price_date, ( SELECT prices_am FROM prices WHERE ( prices_watches_ID = current_ID AND prices_locale = 'US') AND ( prices_date >= DATE_SUB(new_price_date,INTERVAL 30 HOUR) ) ORDER BY prices_date ASC LIMIT 1 ) as old_price, ( SELECT ROUND(((new_price - old_price)/old_price)*100,2) ) as percent_change, ( SELECT (new_price - old_price) ) as absolute_change FROM watches_US LEFT OUTER JOIN prices ON prices.prices_watches_ID = watches_US.watches_ID WHERE ( prices_locale = 'US' ) AND ( prices_am IS NOT NULL ) AND ( prices_am != '' ) HAVING ( old_price IS NOT NULL ) AND ( old_price != 0 ) AND ( old_price != '' ) AND ( absolute_change < 0 ) AND ( prices.prices_date = new_price_date ) ORDER BY absolute_change ASC LIMIT 10 How would I rewrite this to use joins instead, or otherwise optimize this so it doesn't take over 3 minutes to get a result? Any help would be greatly appreciated! Thank you kindly.

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