Rails migrations – change_column with type conversion

If your strings in smoking column are already valid boolean values, the following statement will change the column type without losing data:

change_column :users, :smoking, 'boolean USING CAST(smoking AS boolean)'

Similarly, you can use this statement to cast columns to integer:

change_column :table_name, :column_name, 'integer USING CAST(column_name AS integer)'

I am using Postgres. Not sure whether this solution works for other databases.