Fetch row with shortest date range while dealing with 'infinity'

Question

Consider my schema:

CREATE TABLE t_date (
  t_date_id  int PRIMARY KEY
, valid_from date NOT NULL
, valid_to   date DEFAULT 'infinity'
);

Sometimes I have valid_to dates, sometimes I have infinity there ...
How do I filter properly to get the row with the shortest range?

I tried with:

(DATE_PART('day', valid_to::timestamp - valid_from::timestamp))

But that resulted in:

PG::DatetimeFieldOverflow: ERROR:  cannot subtract infinite timestamps`

I have filters to select the valid range: valid_from <= ? AND valid_to > ?

The idea is to fetch the (one) valid row with the shortest range.

Example

INSERT INTO t_date VALUES
  (1, '2020-01-01', '2020-09-01')
, (2, '2020-01-10', '2020-01-12')
, (3, '2020-01-15', 'INFINITY')
, (4, '2020-01-16', 'INFINITY')  -- shortest among infinities
, (5, '2020-01-14', 'INFINITY')
;

If today is 11/jan I expect to get '2020-01-10' | '2020-01-12' because it's valid for 11/jan and shortest.

If today is 14/jan I expect to get '2020-01-01' | '2020-09-01' because it's valid for 14/jan and shortest.

If today is 17/jan I expect to get '2020-01-16' | 'INFINITY'.
If later I created something like '2020-01-15' | '2059-01-15', that should be returned instead, because it's shorter than the INFINITY row.

I took the liberty to clarify the question as I understood it. (Using proper SQL statements and ISO dates while being at it.) Please fix if I didn't get you right. — Erwin Brandstetter, Jul 08 '20 at 12:37

Erwin Brandstetter · Accepted Answer · 2020-07-08T12:25:19.360

SELECT *
FROM   t_date
WHERE  valid_from <= ?
AND    valid_to   > ?
ORDER  BY NULLIF(valid_to, 'infinity') - valid_from
        , valid_from DESC         -- tiebreaker: later start first
     -- , t_date_id               -- optional additional tiebreaker
LIMIT  1;

db<>fiddle here

NULLIF() converts 'infinity' to NULL, so the whole expression becomes NULL, which sorts last in default ASCENDING order. Infinite ranges should come last for your task.

To break ties among infinite ranges, additionally sort by valid_from DESC - which is defined NOT NULL, so we don't need special treatment for the NULL case. As a (welcome?) side effect, this also breaks ties among other ranges of equal length, picking the latest start.

To get deterministic results, you may want to add another, unambiguous tiebreaker (like the PK column) if identical ranges are allowed.

Sort NULL values to the end of a table

Fetch row with shortest date range while dealing with 'infinity'

Example

1 Answers1