… tables)? For performance, it’s hard to make a general rule, because there are different types of subqueries (correlated, non-correlated, derived tables…-by-case decision. There are other drawbacks to using temporary tables in this way, for example when using replication, a temporary… you’re referring to is what I covered as the Derived-Table Solution on slides 55-59. Apologies if that wasn’t…
Post: Derived Tables and Views Performance
August 31, 2006 By 16 Comments
… in terms of query optimization. Derived Tables are still handled by materializing them in the temporary table, furthermore temporary table with no indexes (so… not want to join two derived tables for example). One more thing to watch for is the fact derived table is going to be… took just to execute explain for derived table So what does it mean in practice: Avoid derived tables – If there is other way to…
Post: MySQL VIEW as performance troublemaker
August 12, 2007 By 57 Comments
…: 1792695 Extra: Using index *************************** 4. row *************************** id: 2 select_type: DERIVED table: comments type: index possible_keys: NULL key: PRIMARY key_len… large derived tables it will become nightmare. So be very careful implementing MySQL VIEWs in your application, especially ones which require temporary table…
Post: Air traffic queries in InfiniDB: early alpha
November 2, 2009 By 19 Comments
… not support DERIVED TABLES, which is big limitation from my point of view. As workaround I tried to create temporary table, but got… DERIVED TABLES, as not supported by InfiniDB. Other queries: (again look on comparison with other engines in Google Spreadsheet or in summary table… can handle, quite often better than InfoBright. Inability to handle derived tables is significant drawback for me, I hope it will be…
Comment: Derived Tables and Views Performance
September 1, 2006 By 16 Comments
Martijn, First – you’re right. There is no reason for derived tables to be materialized. It is design deficiency in MySQL 5… | table | type | possible_keys | key | key_len | ref | rows | Extra | +—-+————-+————+——-+—————+——+———+——+———+————-+ | 1 | PRIMARY | | ALL | NULL | NULL | NULL | NULL | 1638400 | Using where | | 2 | DERIVED…
Comment: Derived Tables and Views Performance
October 19, 2012 By 16 Comments
I experienced this problem on OS X 10.6.8 with the most recent version of MySQL (5.5.27). It still exists. Derived tables (at least for me) are not indexed. I’m no longer using derived tables, and using views (which are indexed) instead.
Comment: A common problem when optimizing COUNT()
September 21, 2008 By 19 Comments
… … I would imagine that the syntax I showed ( using a derived table) would work on most databases. I’m not sure why… completely botched describing was that previous to MySQL having subqueries/derived tables being able to use columns that do not appear in…
Post: 10+ Ways to Crash or Overload MySQL
November 13, 2007 By 20 Comments
… you couple of hints: Temporary Tables You can build query (with derived tables) which uses as many temporary tables as you like and you… is max_heap_table_size to restrict size of each table total size is unrestricted. Note you can create tables as TEMPORARY so…, so this is mainly the problem for smaller servers. Table Cache Merge Tables – Table Cache is allocated in entries and it is normally…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
… 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… not tell much about cost of the operation – full table scan of table in memory may be done at speed of millions…
Post: Hidden columns of query_review_history table
August 28, 2012 By Leave a Comment
… historical values for review trend analysis into query_review_history table. According to its official documentation you can populate many columns…). With creative use of –filter, you can create new attributes derived from existing attributes. Note: the event attributes list could be… have the following useful columns populated in query_review_history table: * `user_max` varchar(64) DEFAULT NULL – User who executed the…
