In this blog post, I’ll look into four ways MySQL executes GROUP BY. 

In my previous blog post, we learned that indexes or other means of finding data might not be the most expensive part of query execution. For example, MySQL GROUP BY could potentially be responsible for 90% or more of the query execution time. 

The main complexity when MySQL executes GROUP BY is computing aggregate functions in a GROUP BY statement. How this works is shown in the documentation for UDF Aggregate Functions. As we see, the requirement is that UDF functions get all values that constitute the single group one …

As I wrote a few days ago, I'm writing the replication chapter for the second edition of High Performance MySQL. I'm writing about replication filtering rules right now, and I thought it would be good to get input on this. If you have favorite replication filtering tricks you'd like to share, or tasks that always frustrate and/or confuse you, please post them in the comments. I'm making a section that shows how to accomplish common filtering and rewriting needs, such as preventing GRANT statements from replicating to the slaves.

Thanks very much! I hope the community involvement will make this book more useful for everyone.