Planet MySQL Planet MySQL: Meta Deutsch Español Français Italiano 日本語 Русский Português 中文
Showing entries 1 to 3

Displaying posts with tag: query optimizer (reset)

Optimizer Trace and EXPLAIN FORMAT=JSON in 5.7
Employee +1 Vote Up -0Vote Down

I accidentally stumbled upon this Stack Overflow question this morning:

I am wondering if there is any difference in regards to performance between the following:

SELECT ... FROM ... WHERE someFIELD IN(1,2,3,4);
SELECT ... FROM ... WHERE someFIELD between  0 AND 5;
SELECT ... FROM ... WHERE someFIELD = 1 OR someFIELD = 2 OR someFIELD = 3 ...;

It is an interesting question because there was no good way to answer it when it was asked in 2009. All of the queries resolve to the same output in EXPLAIN. Here is an example using the …

  [Read more...]
Testing the UNION ALL Optimization in MySQL 5.7 DMR3
Employee +0 Vote Up -0Vote Down

When MySQL 5.7 DMR3 was released, I couldn’t wait to try out the new UNION ALL optimization that no longer requires data to be materialized in a temporary table.

This new optimization can be seen via EXPLAIN, but it is also nice to run it through SHOW PROFILES, which breaks down query execution step by step. However, this feature is now deprecated (since it overlaps with performance_schema), and will be removed in a future version.

So today I wanted to show you a combination of: * What a UNION ALL statement looks like in MySQL 5.6 (EXPLAIN, …

  [Read more...]
Shoot in the foot
+0 Vote Up -0Vote Down

I've just finished reading two recent blog posts about new query optimizations in the upcoming MySQL 6.0, it's all fine and dandy but ...Looking at Correlated semi-join subqueries and PostgreSQL by S. Petrunia we can read something like Quote: The first thing we did was to take a look at PostgreSQL as it is easily available and seems to have at least decent subquery handling (or even better

Showing entries 1 to 3

Planet MySQL © 1995, 2015, Oracle Corporation and/or its affiliates   Legal Policies | Your Privacy Rights | Terms of Use

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.