Re: Electricity bill

On 6/7/22 21:47, David G. Johnston wrote:
> On Tue, Jun 7, 2022 at 6:39 PM Theodore M Rolle, Jr. <stercor@gmail.com 
> <mailto:stercor@gmail.com>> wrote:
> 
>     I'm putting in YYYY-MM-DD dates of electricity bills and would like
>     to not have starting and ending dates in the same row. Only ending date.
>     Will someone show me the SQL to compute the months’ usage? This
>     requires retrieving two rows to compute the number of days...
> 
> You can use a window function called lead (or lag) to retrieve a value 
> from the next (previous) row and associate it with the current row.

Another way that might work for you is interval math and ranges, e.g.:

select enddt, month, year from bill;
              enddt             | month | year
-------------------------------+-------+------
  2021-12-31 23:59:59.999999-05 | dec   | 2021
  2022-01-31 23:59:59.999999-05 | jan   | 2022
  2022-02-28 23:59:59.999999-05 | feb   | 2022
  2022-03-31 23:59:59.999999-04 | mar   | 2022
  2022-04-30 23:59:59.999999-04 | apr   | 2022
  2022-05-31 23:59:59.999999-04 | may   | 2022
  2022-06-30 23:59:59.999999-04 | jun   | 2022
  2022-07-31 23:59:59.999999-04 | jul   | 2022
  2022-08-31 23:59:59.999999-04 | aug   | 2022
  2022-09-30 23:59:59.999999-04 | sep   | 2022
  2022-10-31 23:59:59.999999-04 | oct   | 2022
  2022-11-30 23:59:59.999999-05 | nov   | 2022
  2022-12-31 23:59:59.999999-05 | dec   | 2022
(13 rows)

WITH tsr (tr, month, year) AS
(
  SELECT
   tstzrange(b.enddt - '1 month'::interval,
             b.enddt,
             '(]') AS tr,
   b.month,
   b.year
  FROM
   bill b
)
SELECT tr, month, year
FROM tsr
WHERE now() <@ tr;
-[ RECORD 1 ]----------------------------------------------
tr    | ["2022-05-30 00:00:00-04","2022-06-30 00:00:00-04")
month | jun
year  | 2022

Adjust the open/closed bounds to suit.

HTH,

-- 
Joe Conway
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com