title: switching from Sqlite3 to PostgreSQL on an existing rails application
body: <p>When I tried to switching from sqlite3 to postgresql in my existing application I faced this problem with <code>rake db:migrate</code>, I did the following </p>
  
  <p>1 - rake db:create </p>
  
  <p>2- <code>rake db:migrate</code> I got this error: </p>
  
  <p><code>== AddColumn1: migrating ===================================================== -- add_column(:users, :first_name, :string) rake aborted! An error has occurred, this and all later migrations canceled: PG::Error: ERROR: relation "users" does not exist</code> </p>
  
  <p>3- <code>rake db:reset</code> </p>
  
  <p>4- <code>rake db:migrate</code> , now migration is done with no errors</p>
  
  <p>I have lost my data specially my admin user because of rake db:reset and my questions is :</p>
  
  <p>1- why I forced to use <code>rake db:reset</code> ?</p>
  
  <p>2- is there ways to transfer my data from a database engine to another without losing it in the next time ?</p>
  
  <p>3- and for PostgreSQL I couldn’t use a blank password , it said <code>fe_sendauth: no password supplied</code> , after adding password this error is gone , using password in another database engine instead of Sqlite3 is a must ?</p>
  
  <p>4- will heroku require a reset also or its like Github will accept the data if I use another db engine in development ?</p>