> with details as (
    select tokenize(REGEXP_EXTRACT(text, 'Statement Date: .*'))[3] as month,
    tokenize(REGEXP_EXTRACT(text, 'Statement Date: .*'))[5] as year,
    cast(tokenize(REGEXP_EXTRACT(text, 'Total Amount Due:\n.*\nAmount Enclosed'))[4] as float) as amount
    from "elec-bills"
)
select concat(month, '/', year) as billing_period, amount
from details
order by year asc, month;

+----------+------------------+
| amount   | billing_period   |
|----------+------------------|
| 47.55    | 04/2018          |
| 76.5     | 05/2018          |
| 52.28    | 06/2018          |
| 50.58    | 07/2018          |
| 47.62    | 08/2018          |
| 39.7     | 09/2018          |
| <null>   | 10/2018          |
| 72.93    | 11/2018          |
| 157.57   | 12/2018          |
+----------+------------------+