In Rails2.0.2
rails demo
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MissingSourceFile in SayController # hello
no such file to load - sqlite3
RAILS_ROOT: / home / kenb / rails-projects / demo
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Checked config / database.yml, adpter default is set become the sqlite3.
Check the rails a bit of help:
-d, - database = name Preconfigure for selected database (options: mysql/oracle/postgresql/sqlite2/sqlite3).
Default: mysql
Should be the default seems to mysql, try several times, was set as the default sqlite3
Had no choice but to use-d parameter specifies the database adpter (rails-d mysql demo)

But the problem is in the radrails, and there can specify-d to find the place, but even the manual is also too cumbersome. (Many characters played 8...)
找来找去, finally found the way to default renamed mysql:

ubuntu as an example:
Dir: / usr (var) / lib/ruby/gems/1.8/gems/rails-2.0.2/lib/rails_generator/generators/applications/app
File: app_generator.rb
Line: 11 default_options: db => (ENV [ "RAILS_DEFAULT_DATABASE"] | | "sqlite3"),
Change to: default_options: db => (ENV [ "RAILS_DEFAULT_DATABASE"] | | "mysql"),

Can finally once and for all the, huh, huh ... ...