Generated columns on MySQL 5.7+ and MariaDB 5.2+ are now supported using
the :generated_always_as option when creating the column. The
:generated_type option can also be used to specify the type of generated
column (virtual or stored). Examples:
DB.add_column :t, :c, Integer, generated_always_as: Sequel[:a]+'b'
# ALTER TABLE `t` ADD COLUMN `c` varchar(255)
# GENERATED ALWAYS AS (CONCAT(`a`, 'b'))
DB.add_column :t, :c, Integer, generated_always_as: Sequel[:a]+'b',
generated_type: :virtual
# ALTER TABLE `t` ADD COLUMN `c` varchar(255)
# GENERATED ALWAYS AS (CONCAT(`a`, 'b')) VIRTUAL
DB.add_column :t, :c, Integer, generated_always_as: Sequel[:a]+'b',
generated_type: :stored
# ALTER TABLE `t` ADD COLUMN `c` varchar(255)
# GENERATED ALWAYS AS (CONCAT(`a`, 'b')) STORED