Trying to understand how to use postgresql generate_series() for this operation First of all, im coming from this question, where I was recommended to use generate_series() , but after some adjustments in my db, I dont really understand how to create such sentence
This is the old question: Populate a table that should have an X amount of rows with default values with a big insert query? Or can it done somehow by default?

But I will rephrase the question again:

Those are my initial tables


Users: id(int) PK, weeks_to_live(int)
Calendar: id(int) PK, user_id (int) (FK -> Users(id))*
CalendarField: id(int) PK, text(text), rating(int), calendar_id(int) (FK ->Calendar(id))*, week_number(int)


Point is, when I generate my calendar in my app, actually my Users, and Calendar tables get filled properly.
Upon a generation they will end up looking like this

users

id   weeks_to_live
1    3
2    2


calendar

id   user_id
1    1
2    2


That part is fine, but I need my CalendarField table to be autogenerated too, and thats where supposedly generate_series() should come into action, so they will end up looking like this

CalendarField

id    text     rating    calendar_id   week_number
1     ''       0         1             0
2     ''       0         1             1
3     ''       0         1             2
4     ''       0         2             0
5     ''       0         2             1


As you can observe:


id: is autoincremental
text: always defaults to "",
rating: always defaults to 0,
calendar_id (fk) : is the relation with each calendar, who has an amount of calendarFields row equaling to the number up to weeks_to_live in users
week_number: this number, should begin at 0, and keep incrementing while its &lt; than weeks_to_live in the users table


Now my question is, how do I generate that last insert so my CalendarField table ends up filling with that info?. I suppose that with generate series, I wont need to create an enormous insert with == weeks_to_live values in case it gets huge. But I don't understand how to do it.

Or should I do a giant Insert then?
You need to join users and calendar and then cross join that with a generate_series().

insert into calendar_field (text, rating, calendar_id, week_number)
select '', 0, c.id, g.wn
from calendar c
  join users u on u.id = c.user_id
  cross join generate_series(0, u.weeks_to_live) as g(wn);


Online example