Another UNION ALL query
in [Databases]
|
Prev: Any good explanations of pg_send_execute and friends?
Next: php mysql comparing two rows in two columns for username and passwort
From: "Ron Piggott" on 29 Apr 2010 05:33 I have a 'Highlights' heading on my home page. It is for links to content on the site ... like specific web pages I have designed the query below to select the two most popular and least popular pages used on the site to be the Highlights. (Each time a web page is accessed user_hits is increased by 1.) I would like to display a fifth one that is " ORDER BY RAND () LIMIT 1 " --- Only I don't know how to ensure it isn't one of the four that are being displayed already. Any suggestions? Ron SELECT `highlights`.`reference`, `highlights`.`page_command`, `highlights`.`page_title` FROM ( ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE `include_in_highlights` =1 ORDER BY `user_hits` DESC LIMIT 2 ) UNION ALL ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE `include_in_highlights` =1 ORDER BY `user_hits` ASC LIMIT 2 ) ) AS highlights ORDER BY `highlights`.`page_title` ASC
From: maarten on 29 Apr 2010 11:23 Hi, while I can not help you with your direct question, I don't know of a way to order randomly and select one you hadn't selected yet in SQL, there is another way to do this. With your UNION query your already executing two 'expensive' queries, the entire table get's ordered (twice) before the limits are applied, every time someone goes to your website. Better might be to run just one query: SELECT reference,page_command,page_title,user_hits FROM ... ORDER BY user_hits Then use php to select the first 2 and the last 2, and maybe a random fifth using something like n=randint(2,#rows_returned-2-1) to get the n'th row. (which will exclude the first 2 and last 2 rows) regards, Maarten On Thu, 2010-04-29 at 05:33 -0400, Ron Piggott wrote: > I have a 'Highlights' heading on my home page. It is for links to content > on the site ... like specific web pages > > I have designed the query below to select the two most popular and least > popular pages used on the site to be the Highlights. (Each time a web > page is accessed user_hits is increased by 1.) > > I would like to display a fifth one that is " ORDER BY RAND () LIMIT 1 " > --- Only I don't know how to ensure it isn't one of the four that are > being displayed already. Any suggestions? > > Ron > > > > SELECT `highlights`.`reference`, `highlights`.`page_command`, > `highlights`.`page_title` FROM ( > > ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE > `include_in_highlights` =1 ORDER BY `user_hits` DESC LIMIT 2 ) > > UNION ALL > > ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE > `include_in_highlights` =1 ORDER BY `user_hits` ASC LIMIT 2 ) > > ) AS highlights ORDER BY `highlights`.`page_title` ASC > >
From: "David Murphy" on 29 Apr 2010 12:39
-----Original Message----- From: maarten [mailto:maarten.foque(a)edchq.com] Sent: Thursday, April 29, 2010 10:23 AM To: php-db(a)lists.php.net Subject: Re: [PHP-DB] Another UNION ALL query Hi, while I can not help you with your direct question, I don't know of a way to order randomly and select one you hadn't selected yet in SQL, there is another way to do this. With your UNION query your already executing two 'expensive' queries, the entire table get's ordered (twice) before the limits are applied, every time someone goes to your website. Better might be to run just one query: SELECT reference,page_command,page_title,user_hits FROM ... ORDER BY user_hits Then use php to select the first 2 and the last 2, and maybe a random fifth using something like n=randint(2,#rows_returned-2-1) to get the n'th row. (which will exclude the first 2 and last 2 rows) regards, Maarten On Thu, 2010-04-29 at 05:33 -0400, Ron Piggott wrote: > I have a 'Highlights' heading on my home page. It is for links to content > on the site ... like specific web pages > > I have designed the query below to select the two most popular and least > popular pages used on the site to be the Highlights. (Each time a web > page is accessed user_hits is increased by 1.) > > I would like to display a fifth one that is " ORDER BY RAND () LIMIT 1 " > --- Only I don't know how to ensure it isn't one of the four that are > being displayed already. Any suggestions? > > Ron > > > > SELECT `highlights`.`reference`, `highlights`.`page_command`, > `highlights`.`page_title` FROM ( > > ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE > `include_in_highlights` =1 ORDER BY `user_hits` DESC LIMIT 2 ) > > UNION ALL > > ( SELECT `reference`, `page_command`, `page_title` FROM `user_pages` WHERE > `include_in_highlights` =1 ORDER BY `user_hits` ASC LIMIT 2 ) > > ) AS highlights ORDER BY `highlights`.`page_title` ASC > > -- PHP Database Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php Its very hard to say which is more effective. For example id both include_in_highlights and user_hits are index'ed, it would likely take much more time for MYSQL -> PHP Transimiation of the entire result set than for you to use a union like this. Let assume they are index'ed you could do... CREATE VIEW TopBottomPages AS ( SELECT `id`,`reference`, `page_command`, `page_title` FROM `user_pages` WHERE `include_in_highlights` = 1 ORDER BY `user_hits` DESC LIMIT 2 ) UNION ALL ( SELECT `id`,`reference`, `page_command`, `page_title` FROM `user_pages` WHERE `include_in_highlights` = 1 ORDER BY `user_hits` ASC LIMIT 2 ); SELECT `highlights`.`reference`, `highlights`.`page_command`, `highlights`.`page_title` FROM (SELECT * from TopBottomPages) UNION ALL (SELECT `id` `reference`,`page_command`,`page_title` from `user_pages` where `include_in_hightlights` = 1 and id NOT IN TopBottomPages.id ORDER BY RAND() LIMIT,1) as highlights ORDER BY `highlights`.`page_title` ASC Since you already ran TopBottomPages it would be in the query cache for the NOT IN check. Granted you could do this with a single transaction using just union's if it innodb by im assuming this might be another engine. David |