对于Using filesort，官方解释如下：

If the Extra column of EXPLAIN output does not contain Using filesort, the index is used and a filesort is not performed.

If the Extra column of EXPLAIN output contains Using filesort, the index is not used and a filesort is performed.

对于Using temporary，官方给出了temporary出现的原因：
https://dev.mysql.com/doc/refman/8.0/en/internal-temporary-tables.html

是不是走索引，主要看TYPE和USING INDEX.