…query patterns the optimizer recognizes, and which are left to the developer to refactor manually. There … Couldn’t you have used a SUBQUERY to fetch and compare MAX(episode_id) as an option …Percona Training classes in North America and Europe. Join Percona and the MySQL community at our events….
Comment: Derived Tables and Views Performance
May 21, 2013 By 16 Comments
….id, a.label, a.link, Deriv1.Count FROM `menu` a LEFT OUTER JOIN (SELECT parent, COUNT(*) AS Count FROM `menu` GROUP BY… = Deriv1.parent WHERE a.parent=” . $parent); echo “”; while ($row = mysql_fetch_assoc($result)) { if ($row['Count'] > 0) { echo “” . $row['label'] . “”; display…
Post: Using CHAR keys for joins, how much is the overhead ?
June 18, 2007 By 18 Comments
… query or schema. For joins which fetch just few rows difference is likely to be less as the join code itself is likely…+t2.j+length(t2.c)+t1.j) from intjoin t1 left join intjoin t2 on t1.i=t2.j; +———————————-+ | sum(t1.i…+t2.j+length(t2.c)+t1.j) from intjoin t1 left join intjoin t2 on t1.i=t2.j \G *************************** 1. row…
Post: A case for MariaDB's Hash Joins
May 31, 2012 By Leave a Comment
…_orderdate which results in random scans of the PK to fetch the columns that are not part of the secondary key… are joining tables with no indexes on the join condition (Full Join). The best performance with Hash Join can be achieved when the left table can fit completely in the join buffer…
Comment: ORDER BY ... LIMIT Performance Optimization
July 9, 2007 By 100 Comments
… main query to fetch the actual results: SELECT users.username,bla bla….. FROM whatever LEFT JOIN categories ON category = categories.id LEFT JOIN users ON…,1 SELECT users.username,bla bla FROM whatever LEFT JOIN categories ON category = categories.id LEFT JOIN users ON owner = users.id WHERE visible…
Comment: GROUP_CONCAT useful GROUP BY extension
January 17, 2013 By 49 Comments
…: GROUP_CONCAT is rather slower than a regular while( mysql_fetch_array() ) PHP loop. The example here is just for simplicity…`, `p`.`description`, group_concat( `pf`.`filename` SEPARATOR ‘:’ ) FROM `pages` `p` LEFT JOIN `pages_files` `pf` USING( `pages_id` ) will get all pages…_concat( concat( `pf`.`description`, ‘: ‘, `pf`.`filename` ) SEPARATOR ‘;’ ) FROM `pages` `p` LEFT JOIN `pages_files` `pf` USING( `pages_id` ) to get same as…
Comment: Why MySQL could be slow with large tables ?
January 29, 2009 By 141 Comments
… All i am using mysql I had a problem with joining table where all table had a records more than 2… this with multiple table joing of both type like inner join and left join etc but it was not working and give rows… that 10 minituts so please anybody help me for the fetch row from multiple rows having a more than two lacs…
Post: Eventual Consistency in MySQL
November 18, 2011 By 8 Comments
… find orphaned rows in Bar: SELECT Bar.ID FROM Bar LEFT OUTER JOIN Foo ON (Bar.X,Bar.Y) = (Foo.A,Foo… in KEY_COLUMN_USAGE, we can write a query to fetch every distinct KEY_COLUMN_USAGE.CONSTRAINT_NAME where the REFERENCED….TABLE_SCHEMA, ‘.’, K.TABLE_NAME, ‘ AS ‘, K.CONSTRAINT_NAME, ‘ ‘, ‘LEFT OUTER JOIN ‘, K.REFERENCED_TABLE_SCHEMA, ‘.’, K.REFERENCED_TABLE_NAME, ‘ AS ‘, K…
Post: MySQL VIEW as performance troublemaker
August 12, 2007 By 57 Comments
…to the blog, naturally containing user_id which left comment, comment_id and comment text: CREATE TABLE `comments`…such query and time for the query which fetches everything from the VIEW – it is almost …case which are fully populated and “full join” used to to join between them. In this particular …
Post: SHOW INNODB STATUS walk through
July 17, 2006 By 40 Comments
… important for most diagnostic cases – It is left by Innodb developers so SHOW INNODB STATUS …basically what transaction is doing it can be “fetching rows”, “updating” and couple of other values. “… “waiting in InnoDB queue” or “sleeping before joining InnoDB queue”. Latest one is quite interesting – …
