gitlab-org--gitlab-foss/db/migrate/20150817163600_deduplicate_user_identities.rb

class DeduplicateUserIdentities < ActiveRecord::Migration
  def change
    execute 'DROP TABLE IF EXISTS tt_migration_DeduplicateUserIdentities;'
    execute 'CREATE TABLE tt_migration_DeduplicateUserIdentities AS SELECT id,provider,user_id FROM identities;'
    execute 'DELETE FROM identities WHERE id NOT IN ( SELECT MIN(id) FROM tt_migration_DeduplicateUserIdentities GROUP BY user_id, provider);'
    execute 'DROP TABLE IF EXISTS tt_migration_DeduplicateUserIdentities;'
  end

  def down
    # This is an irreversible migration;
    # If someone is trying to rollback for other reasons, we should not throw an Exception.
    # raise ActiveRecord::IrreversibleMigration
  end
end