Rails UNIQUE INDEX allowing null or empty values

It's a common scenario we need to place a UNIQUE INDEX database constraint for data integrity. But sometime the requirements comes like we need to allow null/empty values for that column.

Enable remote access to PostgreSQL database server

Often it's good to access databases directly from desktop. Or maybe you want your database server to be different from your application server. Whatever your reason is, the requirement is enabling remote access to your PostgreSQL database server.