RAILS DB

db:migrate runs (single) migrations that have not run yet.

db:create creates the database

db:drop deletes the database

db:schema:load creates tables and columns within the existing database following schema.rb. This will delete existing data.

db:setup does db:create, db:schema:load, db:seed

db:reset does db:drop, db:setup

db:migrate:reset does db:drop, db:create, db:migrate

Typically, you would use db:migrate after having made changes to the schema via new migration files (this makes sense only if there is already data in the database). db:schema:load is used when you setup a new instance of your app.

For rails 3.2.12:
I just checked the source and the dependencies are like this now:

db:create creates the database for the current env

db:create:all creates the databases for all envs

db:drop drops the database for the current env

db:drop:all drops the databases for all envs

db:migrate runs migrations for the current env that have not run yet

db:migrate:up runs one specific migration

db:migrate:down rolls back one specific migration

db:migrate:status shows current migration status

db:rollback rolls back the last migration

db:forward advances the current schema version to the next one

db:seed (only) runs the db/seed.rb file

db:schema:load loads the schema into the current env's database

db:schema:dump dumps the current env's schema (and seems to create the db as well)

db:setup runs db:create db:schema:load db:seed

db:reset runs db:drop db:setup

db:migrate:redo runs (db:migrate:down db:migrate:up) or (db:rollback db:migrate) depending on the specified migration

db:migrate:reset runs db:drop db:create db:migrate