Ok, after that you should know how to create a database in PostgreSQL, hook up to a Rails app and run migrations. Once that’s done, you’ll need to be able to do the same things that you were able to do in MySQL in the psql shell. Here’s the first commands you need…

• typing ‘help’ displays help at any time
• \? displays help with psql commands
• \l lists databases
• \c some_database connects to a database
• \c with no argument tells you what database you’re currently connected to
• \ds lists schemas within the currently selected database. A schema is simply a namespacing of tables within a given database
• \dt lists tables in the currently selected database
• \du lists all postgres database user accounts (more detail here)

Here’s  a list of good of stuff…

• The ‘LIKE’ pattern matcher in Postgres is case sensitive (in MySQL it is case insensitive – to get this behaviour in Postgres use ‘ILIKE’)
• What are schemas in PostgreSQL?
• If you want to keep things simple, just forget about schemas and everything will end up in a ‘public’ schema (but you should read about schemas briefly so that they don’t drive you mad when administering your postgres database)
• Postgres Gotchas
• Switching from MySQL to PostgreSQL – tips, tricks and gotchas?

2) In your config/database.yml file, point at the database you wish to dump to a migrations file

3) Run the command ‘rake db:schema:dump’. This should create a db/schema.rb file. Amazingly this effectively is your migrations file!

4) To tidy up create a file called file db/migrate/20091125205635_create_initial_schema.rb

5) Then copy the create_table statements from the schema.rb file into the new file 20091125205635_create_initial_schema.rb. Here’s a template

class CreateInitialSchema < ActiveRecord::Migration

  def self.up
    # Put all create_table statements from schema.rb file here
    # Note: You don't need the 'ActiveRecord::Schema.define(:version' line or it's enclosing end statement
    # ...
    # ...
  end

  def self.down
    # Don't really need this
  end

end

6) Once you’ve all this done you can just run ‘rake db:migrate’ and you should have a new sqlite db up and running under db/development.sqlite3

Thanks to Justin Ball on this Nobody Listens Anyway blog at Dump an Existing Database Schema Into a Ruby On Rails Migration Ready Format for the basis of this tip. Sometimes somebody does…