rake db：migrate的问题

Question

I am beginner for this Rails . I am working hard to fix the following error

C:\library>rake db:migrate --trace
(in C:/library)
** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:migrate
==  CreateBooks: migrating
====================================================
-- create_table(:books)
rake aborted!
An error has occurred, all later migrations canceled:

Mysql::Error: Table 'books' already exists: CREATE TABLE `books` (`id`
int(11) D
EFAULT NULL auto_increment PRIMARY KEY, `created_at` datetime,
`updated_at` date
time) ENGINE=InnoDB

I manual dropped all the tables that didn't fix the problem Now used rake db:drop db:create db:migrate but still geting rake aborted message..

C:\library>rake db:drop db:create db:migrate

(in C:/library)
rake aborted!
Mysql::Error: Specified key was too long; max key length is 767 bytes: 
CREATE UN
IQUE INDEX `unique_schema_migrations` ON `schema_migrations` (`version`)

Also i dont have schema.rb file.

Answer 1

The first message is probably the result of a migration that failed but wasn't properly backed out. It's a good idea to take a snapshot of your database before you perform migrations so you can restore to a known-good configuration if it messes up.

The second message indicates you're trying to create an index on a field that's "too big" for MySQL to do this. Due to the way MySQL handles UTF-8 characters, each character is allocated three bytes of key space. This means anything longer than 255 characters needs to be given a length limit or it won't work, at least in versions of MySQL that complain about it.

What does seem odd is that it's trying to build the schema_migrations table and failing. Is there anything unusual about your MySQL configuration that might trigger this? Is it an older version? 5.5 or better is recommended.