BigQuery: 'join lateral' alternative for referencing value in subquery - google-bigquery

Question

I have a BigQuery table that holds append-only data - each time an entity is updated a new version of it is inserted. Each entity has its unique ID and each entry has a timestamp of when it was inserted.
When querying for the latest version of the entity, I order by rank, partition by id, and select the most recent version.
I want to take advantage of this and chart the progression of these entities over time. For example, I would like to generate a row for each day since Jan. 1st, with a summary of the entities as they were on that day. In postgres, I would do:
select
...
from generate_series('2022-01-01'::timestamp, '2022-09-01'::timestamp, '1 day'::interval) query_date
left join lateral (
select *
from (
with snapshot as (
select distinct on (id) *
from table
where "createdOn" <= query_date
order by id, "createdOn" desc
)
This basically behaves like a for-each, having each subquery run once for each query_date (day, in this instance) which I can reference in the where clause. Each subquery then filters the data so that it only uses data up to a certain time.
I know that I can create a saved query for the "subquery" logic and then schedule a prefill to run once for each day over the timeline, but I would like to understand how to write an exploratory query.
EDIT 1
Using a correlated subquery is a step in the right direction, but does not work when the subquery needs to join with another table (another append-only table holding a related entity).
So this works:
select
day
, (
select count(*)
from `table` t
where date(createdOn) < day
)
from unnest((select generate_date_array(date('2022-01-01'), current_date(), interval 1 day) as day)) day
order by day desc
But if I need the subquery to join with another table, like in:
select
day
, (
select as struct *
from (
select
id
, status
, rank() over (partition by id order by createdOn desc) as rank
from `table1`
where date(createdOn) < day
qualify rank = 1
) t1
left join (
select
id
, other
, rank() over (partition by id order by createdOn desc) as rank
from `table2`
where date(createdOn) < day
qualify rank = 1
) t2 on t2.other = t1.id
)
from unnest((select generate_date_array(date('2022-01-01'), current_date(), interval 1 day) as day)) day
order by day desc
I get an error saying Correlated subqueries that reference other tables are not supported unless they can be de-correlated, such as by transforming them into an efficient JOIN. Another SO question about that error (Avoid correlated subqueries error in BigQuery) solves the issue by moving the correlated query to a join in the top query - which misses what I am trying to achieve.

Answer 1

Took me a while, but I figured out a way to do this using the answer in Bigquery: WHERE clause using column from outside the subquery.
Basically, it requires to flip the order of the queries, here's how it's done:
select *
from (
select *
from `table1` t1
JOIN (select day from unnest((select generate_timestamp_array(timestamp('2022-01-01'), current_timestamp(), interval 1 day) as day)) day) day
ON (t1.createdOn) < day.day
QUALIFY ROW_NUMBER() OVER (PARTITION BY day, t1.id ORDER BY t1.createdOn desc) = 1
)
left join (
select
* -- aggregate here
from (
SELECT
id, other, createdOn
FROM `table2` t2
JOIN (select day from unnest((select generate_timestamp_array(timestamp('2022-01-01'), current_timestamp(), interval 1 day) as day)) day) day
ON (t2.createdOn) < day.day
QUALIFY ROW_NUMBER() OVER (PARTITION BY day, t2.id ORDER BY t2.createdOn desc) = 1
) snapshot
group by rs.other, day
) t2 on t2.other = t1.id and t2.day = t1.day
group by t1.day