… tables)? For performance, it’s hard to make a general rule, because there are different types of subqueries (correlated, non-correlated, derived tables… upcoming Percona Training classes in North America and Europe. Join Percona and the MySQL community at our events. The next one is…
Post: Derived Tables and Views Performance
August 31, 2006 By 16 Comments
Starting MySQL 4.1, MySQL had support for what is called derived tables, inline views or basically subselects in the from clause. In MySQL 5… do not want to join two derived tables for example). One more thing to watch for is the fact derived table is going to be… | +—+———————————-+ 1 row in set (0.03 sec) Same query using derived table crawls: mysql> select * from (select * from test) t where i=5…
Post: MySQL VIEW as performance troublemaker
August 12, 2007 By 57 Comments
… as with subqueries and derived tables MySQL 5.0 will fail and perform very inefficiently in many counts. MySQL has two ways of handling… “join cache” is used to perform it relatively efficient, however for large derived tables it will become nightmare. So be very careful implementing MySQL…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
… In MySQL 5.0 with addition of greedy join the problem on looking at too many table join combinations in joins with very large tables is elevated, however there are still cases when it may take too long. Most practically important one is if Derived tables (selects in FROM clause) are used. MySQL will execute these subselects on explain to…
Comment: Why MySQL could be slow with large tables ?
December 4, 2008 By 141 Comments
Morten, The problem is you’re joining “derived tables” which causes MySQL to create tables without indexes which causes very slow joins. Known feature limitation, though annoying one.
Post: A workaround for the performance problems of TEMPTABLE views
May 19, 2010 By 7 Comments
…table such that a scan of all rows takes a second or two. mysql> show create table t2\G *************************** 1. row *************************** Table: t2 Create Table: CREATE TABLE… v1 join params p…1 | | | 2 | DERIVED | p | const | PRIMARY | PRIMARY | 260 | | 1 | | | 2 | DERIVED | t2 | ref …
Post: Database problems in MySQL/PHP Applications
August 11, 2006 By 13 Comments
… Why MySQL Could be slow with Large Tables article. 5. The n+1 pattern This probably should rather be called Not using Join. This is typical error. On other hand in MySQL you might be better of using… they are not, and so using IN() list of values derived by previous query. For example you can do: SELECT id…
Comment: Database problems in MySQL/PHP Applications
August 11, 2006 By 13 Comments
…etc. Read more in my > Why MySQL Could be slow with Large Tables article. Deciding whether or not to … not, and so using IN() list of values derived > by previous query. For example you can do: > … to join rows together, potentially preventing a table scan. The trick is to know what kind of JOIN to …
