Create a database.
drush sql-create
--db-su : Account to use when creating a new database. Optional.
--db-su-pw : Password for the "db-su" account. Optional.
Create the database for the current site.
drush sql-create
Create the database as specified for @site.test.
drush @site.test sql-create
Create the database as specified in the db-url option.
drush sql-create --db-su=root --db-su-pw=rootpassword --db-url="mysql://drupal_db_user:drupal_db_password@127.0.0.1/drupal_db"