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Displaying posts with tag: query optimizer (reset)

Testing the UNION ALL Optimization in MySQL 5.7 DMR3
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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, SHOW PROFILES). * How it is improved in MySQL 5.7 (EXPLAIN, SHOW PROFILES). * How you can easily emulate the SHOW PROFILES feature with performance_schema +

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Shoot in the foot
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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 2

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