Classify unnest elements in PostgreSQL - sql

Question

I'm using PostgreSQL 10.6 and i want to read a table with an array of dates. My goal is to classify each date in this array and compare it to the date of the day, to affect them a category : past, present, futur.
With a case statment i've already classify records depending of their values and in the other hand i'm able to unnest elements from this array. But when i try a case statement in unnest elements, response isn't what i'm expecting.
myTable
id(integer) | dates(date[])
---------------------------
1 | {2020-03-17}
2 | {2020-03-17,2020-03-16}
3 | {2020-03-16,2020-03-15}
4 | {2020-03-17,2020-03-18}
5 | {2020-03-16,2020-03-18}
An simple query return me each date in a distinct row
SELECT id, UNNEST(dates) FROM myTable
An other query return me a result by not a good one, because some dates in the past are displayed "Futur" for example.
SELECT
id,
UNNEST(dates),
CASE
WHEN dates < ARRAY[now()::date] THEN 'Past'
WHEN dates = ARRAY[now()::date] THEN 'Present'
WHEN dates > ARRAY[now()::date] THEN 'Futur'
END AS myResult
FROM myTable
ORDER BY UNNEST(dates) DESC
How can i succeed to this result ? I think i'm missing something important.
id | dates | myResult
--------------------------------
4 | {2020-03-18} | Futur
5 | {2020-03-18} | Futur
1 | {2020-03-17} | Present
2 | {2020-03-17} | Present
4 | {2020-03-17} | Present
2 | {2020-03-16} | Past
3 | {2020-03-16} | Past
5 | {2020-03-16} | Past
3 | {2020-03-15} | Past

Answer 1

You need to unnest in the from clause - then you can classify in the from clause:
SELECT
t.id,
d.dt,
CASE
WHEN d.dt < current_date THEN 'Past'
WHEN d.dt = current_date THEN 'Present'
WHEN d.dt > current_date THEN 'Futur'
END AS myResult
FROM myTable t
CROSS JOIN LATERAL UNNEST(t.dates) d(dt)
ORDER BY t.id, d.dt DESC
Demo on DB Fiddle:
id | dt | myresult
-: | :--------- | :-------
1 | 2020-03-17 | Present
2 | 2020-03-17 | Present
2 | 2020-03-16 | Past
3 | 2020-03-16 | Past
3 | 2020-03-15 | Past
4 | 2020-03-18 | Futur
4 | 2020-03-17 | Present
5 | 2020-03-18 | Futur
5 | 2020-03-16 | Past