使用mysql在raes中運行rake db：migrate失敗（表已存在）

Question

我在開發Rails方面相對較新。

我正在嘗試使用以下命令遷移新創建的表：

$ rake db:migrate

但我不斷收到與該表有關的錯誤。 但是，每當我嘗試運行Rails應用程序時，都會收到“遷移未完成”錯誤。

我不介意刪除該表，因為我才剛剛開始使用此應用程序，因此刪除了以前的遷移，並且運行了db：migrate命令，沒有任何要遷移的內容。 然后，我將使用以下命令再次添加新模型：

$ rails generate model User name:string

這給了我預期的輸出：

    invoke  active_record
      create    db/migrate/20141129134103_create_users.rb
   identical    app/models/user.rb
      invoke    test_unit
   identical      test/models/user_test.rb
   identical      test/fixtures/users.yml

但是之后，我運行：

$ rake db:migrate --trace

我得到以下輸出：

** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:migrate
== 20141129134103 CreateUsers: migrating ======================================
-- create_table(:users)
rake aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Table 'users' already exists: CREATE TABLE `users` (`id` int(11) auto_increment PRIMARY KEY, `name` varchar(255), `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'users' already exists: CREATE TABLE `users` (`id` int(11) auto_increment PRIMARY KEY, `name` varchar(255), `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
Mysql2::Error: Table 'users' already exists
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
Tasks: TOP => db:migrate

就像我說的那樣，在運行Rails應用程序后，我得到“遷移即將發生”錯誤，而且我似乎無法理解出了什么問題。 讓我知道您是否需要其他文件來幫助診斷此問題。 我做的與教程不同的一件事是，我在數據庫中使用mysql而不是sqlite3。

先感謝您 ：）

Answer 1

您正在刪除遷移，在軌道中。 但是，實際的mysql表本身並未被觸摸（刪除），然后您的大多數問題是由於兩者不同步而引起的。

在這種情況下，通常可以選擇：

- `rake db:migrate:down` # To have rails remove the table and keep in sync*

- delete ('drop table users') the table in mysql and then re-run the migrations.

- Use rake db:reset as indicated by jykim to drop the database.

• 'schema_migrations表跟蹤這些內容，因此您也可以進行檢查。

展望未來，不要只刪除遷移而不考慮實際的數據庫表。 使用rails down遷移和db reset使您的mysql db保持同步。 最終，需要正確的schema_migrations表。