问题
It's not explicitly mentioned in the documentation (http://dev.mysql.com/doc/refman/6.0/en/drop-table.html). I ask because I just saw a curious database migration in a Rails project where the developer was removing all the indexes before dropping the table, and that seemed unnecessary.
回答1:
Yes, it does.
However, if you have foreign key constraints such as RESTRICT that ensure referential integrity with other tables, you'll want to drop those keys prior to dropping or truncating a table.
回答2:
Yes it would drop the index. There's no reason to keep the index if the underlying table isn't there. I suspect that the downward migration is just doing the opposite of the upward migration on a one-to-one basis.
回答3:
It is unneccessary. Your DROP TABLE might however be prevented when the table is part of foreign key relationships and dropping your table would break the dependencies.
来源：https://stackoverflow.com/questions/887590/does-dropping-a-table-in-mysql-also-drop-the-indexes