Emergency

Search Results for: mysql derived select_type

MySQL VIEW as performance troublemaker

I start to see applications being built utilizing VIEWs functionality which appeared in MySQL 5.0 and quite frequently VIEWs are used to help in writing the queries – to keep queries simple without really thinking …

Read More
 

Derived Tables and Views Performance

Starting MySQL 4.1, MySQL had support for what is called derived tables, inline views or basically subselects in the from clause. In MySQL 5.0 support for views was added. These features are quite related to …

Read More
 

MySQL EXPLAIN limits and errors.

Running EXPLAIN for problematic queries is very powerful tool for MySQL Performance optimization. If you’ve been using this tool a lot you probably noticed it is not always provide adequate information. Here is list of …

Read More
 

Percona Toolkit collection: pt-visual-explain

This is the first in a series of posts highlighting a few of the seldom-used but still handy Percona Toolkit tools. Have you ever had a problem understanding the EXPLAIN statement output? And are you …

Read More
 

SELECT UNION Results INTO OUTFILE

Here’s a quick tip I know some of us has overlooked at some point. When doing SELECT … UNION SELECT, where do you put the the INTO OUTFILE clause? On the first SELECT, on the …

Read More
 

A workaround for the performance problems of TEMPTABLE views

MySQL supports two different algorithms for views: the MERGE algorithm and the TEMPTABLE algorithm. These two algorithms differ greatly. A view which uses the MERGE algorithm can merge filter conditions into the view query itself. …

Read More
 

Another look at improving TPC-H-like queries – Q17

Summary: An alternate approach, offered in response to our original post, provides excellent improvements for smaller databases, but clustered indexes offer better performance as database size increases. (This posting is by Dave.) Jay Pipes suggested …

Read More