打开PGadmin查看是否有任何查询页面打开，关闭所有查询页面，断开PostgresSQL服务器连接，重新连接，尝试删除/删除选项。这对我很有帮助。

OSX, Postgres 9.2(已安装自制程序)

$ launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
$ pg_ctl restart -D /usr/local/var/postgres
$ launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

如果你的datadir在其他地方，你可以通过检查ps aux | grep postgres的输出来找到它

更简单和更新的方法是:

使用ps -ef | grep postgres找到连接# 须藤杀死-9“#”的连接

注:可能有相同的PID。杀死一个人就会杀死所有人。

没有必要放弃。只需删除并重新创建公共模式。在大多数情况下，这有完全相同的效果。

namespace :db do

desc 'Clear the database'
task :clear_db => :environment do |t,args|
  ActiveRecord::Base.establish_connection
  ActiveRecord::Base.connection.tables.each do |table|
    next if table == 'schema_migrations'
    ActiveRecord::Base.connection.execute("TRUNCATE #{table}")
  end
end

desc 'Delete all tables (but not the database)'
task :drop_schema => :environment do |t,args|
  ActiveRecord::Base.establish_connection
  ActiveRecord::Base.connection.execute("DROP SCHEMA public CASCADE")
  ActiveRecord::Base.connection.execute("CREATE SCHEMA public")
  ActiveRecord::Base.connection.execute("GRANT ALL ON SCHEMA public TO postgres")
  ActiveRecord::Base.connection.execute("GRANT ALL ON SCHEMA public TO public")
  ActiveRecord::Base.connection.execute("COMMENT ON SCHEMA public IS 'standard public schema'")
end

desc 'Recreate the database and seed'
task :redo_db => :environment do |t,args|
  # Executes the dependencies, but only once
  Rake::Task["db:drop_schema"].invoke
  Rake::Task["db:migrate"].invoke
  Rake::Task["db:migrate:status"].invoke 
  Rake::Task["db:structure:dump"].invoke
  Rake::Task["db:seed"].invoke
end

end

退出postgres并重新启动。很简单，但每次对我都有效，而其他cli命令有时不能。

可以使用pg_terminate_backend()终止连接。你必须是超级用户才能使用这个功能。这在所有操作系统上都是一样的。

SELECT 
    pg_terminate_backend(pid) 
FROM 
    pg_stat_activity 
WHERE 
    -- don't kill my own connection!
    pid <> pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'database_name'
    ;

在执行这个查询之前，你必须撤销CONNECT权限以避免新的连接:

REVOKE CONNECT ON DATABASE dbname FROM PUBLIC, username;

如果你正在使用Postgres 8.4-9.1，请使用procpid而不是pid

SELECT 
    pg_terminate_backend(procpid) 
FROM 
    pg_stat_activity 
WHERE 
    -- don't kill my own connection!
    procpid <> pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'database_name'
    ;