1、 extra用于存放无法归入其他类别的关键附加信息。 2、 当extra字段显示为Using filesort时，表示MySQL未利用表内索引顺序读取数据，而是通过外部排序方式对结果进行排序，这种操作被称为文件排序。由于该过程效率较低，会显著影响查询性能，属于需要重点关注 ...

MySQL's Workbench licensing decision really isn't much of a question of proprietary versus open source. It's about speed of development. Matt Asay is a veteran technology columnist who has written for ...