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(at)gmail(dot)com
> <mailto:stercor(at)gmail(dot)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