ALTER TABLE dies with an error like this:
Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17)
The problem may be that MySQL has crashed in a previous
TABLE and there is an old table named `A-something' or
`B-something' lying around. In this case, go to the MySQL data
directory and delete all files that have names starting with
B-. (You may want to move them elsewhere instead of deleting them).
ALTER TABLE works the following way:
- Create a new table named `A-xxx' with the requested changes.
- All rows from the old table are copied to `A-xxx'.
- The old table is renamed `B-xxx'.
- `A-xxx' is renamed to your old table name.
- `B-xxx' is deleted.
If something goes wrong with the renaming operation, MySQL tries to
undo the changes. If something goes seriously wrong (this shouldn't happen,
of course), MySQL may leave the old table as `B-xxx' but a
simple rename should get your data back.