当我运行rake db：migrate时，我得到以下输出：

== 20141219011612 CreatePost: migrating =======================================
-- create_table("posts") rake aborted! StandardError: An error has occurred, this and all later migrations canceled:
== 20141219011612 Postposts: migrating =======================================
-- create_table("posts") rake aborted! StandardError: An error has occurred, this and all later migrations canceled:

PG::DuplicateTable: ERROR: relation"posts" already exists : CREATE
TABLE"posts" ("id" serial primary key,"post" text,"release_date"
timestamp,"created_at" timestamp,"updated_at" timestamp)
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
async_exec'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
block in execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in block in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in
instrument'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:127:in
execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in
create_table'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in
block in method_missing'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
block in say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in
method_missing'
/home/admin/Desktop/postr/db/migrate/20141219011612_post_posts.rb:3:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:598:in
exec_migration'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in
block (2 levels) in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in
with_connection'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in
block in execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
block in ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
block in transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:209:in
within_new_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/transactions.rb:208:intransaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in
execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
each'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in
block (2 levels) in ' ActiveRecord::StatementInvalid:
PG::DuplicateTable: ERROR: relation"posts" already exists : CREATE
TABLE"posts" ("id" serial primary key,"post" text,"release_date"
timestamp,"created_at" timestamp,"updated_at" timestamp)
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
async_exec'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
block in execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in block in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in
instrument'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:127:in
execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in
create_table'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in
block in method_missing'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
block in say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in
method_missing'
/home/admin/Desktop/postr/db/migrate/20141219011612_post_posts.rb:3:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:598:in
exec_migration'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in
block (2 levels) in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in
with_connection'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in
block in execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
block in ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
block in transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:209:in
within_new_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/transactions.rb:208:intransaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in
execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
each'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in
block (2 levels) in ' PG::DuplicateTable: ERROR:
relation"posts" already exists
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
async_exec'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in
block in execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in block in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in
instrument'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in log'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:127:in
execute'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in
create_table'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in
block in method_missing'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
block in say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in
say_with_time'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in
method_missing'
/home/admin/Desktop/postr/db/migrate/20141219011612_post_posts.rb:3:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:598:in
exec_migration'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in
block (2 levels) in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in
with_connection'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in
block in execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
block in ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
block in transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:209:in
within_new_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/database_statements.rb:201:in
transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/transactions.rb:208:intransaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:1037:in
ddl_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in
execute_migration_in_transaction'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in
block in migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
each'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in
up'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in
migrate'
/home/admin/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in
block (2 levels) in ' Tasks: TOP => db:migrate (See
full trace by running task with --trace)

我不知道这是怎么可能的，因为在方案文件中我没有邮政表。

不知何故，您最终在数据库中找到了一个名为"posts"的表。也许是从您之前的迁移中删除而没有回滚？如果您不关心数据库中的任何数据，则可以运行

使您的开发数据库与您当前的迁移一致。

如果您不希望丢失其他表中的数据，请打开数据库控制台并手动删除posts表：

然后再次运行db:migrate。

我发现的一个黑客是在你在迁移文件上创建表之前放入pry。

并删除该表：

之后，您可以删除drop_table行，它将正常工作！

如果这有助于其他任何人，我意识到我一直在使用在使用MySQL时生成的schema.rb文件。转换到Postgres之后，我忘记了在使用rake db:schema:load之前我需要运行rake db:migrate

检查db / schema.rb

除了db / migrate / [timestamp] your_migration中的迁移之外，您很可能在那里创建了相同的表

您可以删除db / migrate / [timestamp] your_migration，如果它与模式中找到的重复并且它应该有效。