我不确定为什么会遇到这个错误。我已经正确设置了PostgreSQL，只是运行了迁移，并执行 rake db:migrate 后出现了该标题错误。
以下是我的：
database.yml
development:
adapter: postgresql
encoding: unicode
database: my_blog_development
pool: 5
username: my_blog
password:
test:
adapter: postgresql
encoding: unicode
database: my_blog_test
pool: 5
username: my_blog
password:
production:
adapter: postgresql
encoding: unicode
database: my_blog_production
pool: 5
username: my_blog
password:
完整错误信息：
[my_blog]$rake db:migrate
rake aborted!
PG::Error: ERROR: permission denied for relation schema_migrations
: SELECT "schema_migrations".* FROM "schema_migrations"
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/postgresql_adapter.rb:739:in `exec'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/postgresql_adapter.rb:739:in `exec_no_cache'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/postgresql/database_statements.rb:138:in `block in exec_query'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/abstract_adapter.rb:425:in `block in log'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activesupport-4.0.0.rc1/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/abstract_adapter.rb:420:in `log'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/postgresql_adapter.rb:856:in `select'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/abstract/database_statements.rb:24:in `select_all'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/querying.rb:36:in `find_by_sql'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/relation.rb:561:in `exec_queries'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/relation.rb:447:in `load'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/relation.rb:196:in `to_a'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/relation/delegation.rb:12:in `map'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:770:in `get_all_versions'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:928:in `migrated'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:933:in `ran?'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:910:in `block in runnable'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:910:in `reject'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:910:in `runnable'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:887:in `migrate'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:747:in `up'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/migration.rb:725:in `migrate'
/usr/local/rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/railties/databases.rake:42:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:246:in `call'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:246:in `block in execute'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:241:in `each'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:241:in `execute'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:184:in `block in invoke_with_call_chain'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:177:in `invoke_with_call_chain'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/task.rb:170:in `invoke'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:143:in `invoke_task'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:101:in `block (2 levels) in top_level'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:101:in `each'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:101:in `block in top_level'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:110:in `run_with_threads'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:95:in `top_level'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:73:in `block in run'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:160:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-2.0.0-p195@global/gems/rake-10.0.4/lib/rake/application.rb:70:in `run'
/usr/local/rvm/gems/ruby-2.0.0-p195/bin/ruby_noexec_wrapper:14:in `eval'
/usr/local/rvm/gems/ruby-2.0.0-p195/bin/ruby_noexec_wrapper:14:in `<main>'
Tasks: TOP => db:migrate