It is wonderful to see some of my original pet peeves fixed in MySQL 5.7.3! It has not even taken 10 years
I remember when starting my work at MySQL Support that I would recommend using UNION ALL instead of plain UNION because it would not require duplicate elimination, and as such, would not require the creation of a temporary table in basic cases. Guess what? MySQL actually did it anyway. The learning experience from this incident was to never use common sense alone when thinking about MySQL – test and validate your assumptions because for one reason or another things may work differently from what “obviously makes sense.” I do not want to single out MySQL – this approach has helped me to be successful with problem analyses of all kinds of software.
The Multi Column IN optimization is another one that …[Read more]