What is the meaning of Select tables optimized away in MySQL Explain plan? explain select count(comment_count) from wp_posts;. When all tables are processed, MySQL outputs the selected columns and backtracks through the table list until a table is found for which there are more matching rows. Select tables optimized away. MySQL can optimize aggregate functions like MIN and MAX as long as the columns specified are indexed. Extra: Select tables optimized away.
Innodb will however need to perform full table scan or full index scan because it does not have such counter, it also can’t be solved by simple singe counter for Innodb tables as different transactions may see different number of rows in the table. NULL NULL NULL NULL NULL NULL Select tables optimized away. Select tables optimized away. The query contained only aggregate functions (MIN(), MAX()) that were all resolved using an index, or COUNT( ) for MyISAM, and no GROUP BY clause. Josh, This was 5.0.77 on Ubuntu 9.04 The storage engine was InnoDB. Jay Pipes says. The same won’t happen on other storage engines in MySQL such as InnoDB.
SELECT count() is so common so it is partly optimized away. (1 reply) I’m converting a table to innodb from myisam in mysql 4.0 and I was wondering why it takes sooo long to do a SELECT COUNT( ) In the old MyISAM table, it’s quick: mysql select count( ) from forecast; +———–+ +———–+ 1 row in set (0. Select tables optimized away. Note: The database is MySQL 5.7.1 and using InnoDB engine. EDIT:.
For Innodb Tables
That’s way the MySQL Query Optimizer optimizes away all standard mechanisms and gives you a row count. Then, convert all your MyISAM tables to InnoDB. Do I have to run optimize table, even though I’m not using delete quick? Name,Engine,Version,Row_format,Rows,Avg_row_length,Data_length,Max_data_length,Index_length,Data_free,Auto_increment,Create_time,Update_time,Check_time,Collation,Checksum,Create_options,Comment order,InnoDB,10,Compact,568037197,280,159252496384,0,180806041600,37692112896,4052226884, 2015-01-26 17:27:20,NULL,NULL,utf8_general_ci,NULL,, The result from select count( ) from order is 618376777 rows. The EXPLAIN said ‘optimized away’ because it could see that it did not need to do any work. Query Performance Optimization In the previous chapter, we explained how to optimize a schema, which is one of the necessary conditions for high performance. Locks that are implemented by the storage engine, such as InnoDB’s row locks, do not cause the thread to enter the Locked state. I couldn’t read this and let it stand because this list is really, really bad. CREATE TABLE posts ( id int unsigned not null auto_increment, author_id int unsigned not null, created timestamp not null, PRIMARY KEY(id) ); CREATE TABLE posts_data ( post_id int unsigned not null. None. Any decent DBMS is going to optimize these away. MySQL has two primary storange engines: MyISAM and InnoDB. A derived table that is embedded in the query is sometimes called an unnamed derived table. The query execution time seems to be affected by home ambiguous the LIKE string’s are.
Mysql To Massive Performance Hit
Try to create an Aria or MyISAM table, INSERT some data, and execute an EXPLAIN similar to the following:. InnoDB cannot optimize away the tables from these queries, because it has a more complex way to handle data. Since the tables are InnoDB, the clustered index is the primary key. What I wanted: keep archive data in a compact, non modifiable table (I chose packed MyISAM tables), and live data in a transactional table (I chose InnoDB), possibly even on two different machines. I was thrilled when I found the article linked above, with the sweet idea how to create a view which would combine both, and imagined that while it would make a performance hit, it shouldn t be that bad, because the data in the packed, optimised MyISAM tables should have much faster access than the InnoDB, and given that the volume of the data is in there, and all select conditions are on indexed columns, it should be pretty fast.