Postgresql: Gaps Between tsranges, empty set - sql

Question

I have a tables of reservations for each user:
reservations_development=# \d reservations
Table "public.reservations"
Column | Type | Modifiers
------------+---------+-----------------------------------------------------------
id | integer | not null default nextval('reservations_id_seq'::regclass)
user_id | integer |
occurrence | tsrange |
Indexes:
"reservations_pkey" PRIMARY KEY, btree (id)
"reservations_occurrence_user_id_excl" EXCLUDE USING gist (occurrence WITH &&, user_id WITH =)
I am trying to create a view of the gaps/opening between reservations for each user, and I currently have the following query:
CREATE OR REPLACE VIEW reservation_gaps AS (
with user_mins as (select tsrange(LOCALTIMESTAMP, min(lower(occurrence))), user_id
FROM (
SELECT user_id, occurrence
FROM reservations
WHERE lower(occurrence) >= LOCALTIMESTAMP
) as y
GROUP BY user_id
),
gaps as (select
tsrange(upper(occurrence), lead(lower(occurrence),1, LOCALTIMESTAMP + interval '1 year') over (win_user_gaps)),
user_id
from (
select user_id, occurrence
from reservations
) as x
WINDOW win_user_gaps AS (PARTITION BY user_id ORDER BY occurrence)
UNION ALL SELECT * FROM user_mins
)
select *
FROM gaps
ORDER BY user_id, tsrange
);
It currently gives the expected results as long as the user has one reservation, but if the user is new, and has not currently been reserved I get an empty result.
I need to in some way append a {tsrange(LOCALTIMESTAMP, LOCALTIMESTAMP + interval '1 year'), user_id} row to the view for each user without a reservation, but I'm currently stumped as to how to do that.
Thanks

Answer 1

You should change the CTE to be a UNION ALL with the artificial rows and then use DISTINCT ON to select one row per user.
with user_mins as (SELECT DISTINCT ON (user_id) user_id, tsrange FROM(
select tsrange(LOCALTIMESTAMP, min(lower(occurrence))) as tsrange, user_id, 1 as priotity
FROM (
SELECT user_id, occurrence
FROM reservations
WHERE lower(occurrence) >= LOCALTIMESTAMP
) as y
GROUP BY user_id
UNION ALL
SELECT user_id, tsrange(LOCALTIMESTAMP, LOCALTIMESTAMP + interval '1 year'),
0
FROM users)
ORDER BY user_id, priority DESC
)

Answer 2

SQL Fiddle
with this_year as (
select tsrange(
date_trunc('year', current_date)::timestamp,
date_trunc('year', current_date)::timestamp + interval '1' year, '[)'
) as this_year
), gaps as (
select
user_id,
this_year - tsrange(lower(occurrence), 'infinity', '[]') lower_range,
this_year - tsrange('-infinity', upper(occurrence), '[]') upper_range,
this_year
from
reservations
cross join
this_year
)
select *
from (
select
user_id,
upper_range *
lead (lower_range, 1, this_year)
over (partition by user_id order by lower_range, upper_range)
as gap
from gaps
union (
select distinct on (user_id)
user_id,
tsrange(
lower(this_year),
coalesce(upper(lower_range), upper(this_year)),
'[)'
) as gap
from gaps
order by user_id, lower_range
)
) s
where gap != 'empty'
order by user_id, gap