Logical Grouping in Bigquery - group-by

Question

I am trying to group data in bigquery that goes beyond simple aggregation. However I am not sure if what I'm trying to do is possible.
The idea behind the data:
One employee will be logged in and can perform multiple transactions. hits.eventInfo captures all of this data but the only field that separates the transactions from one another is a flight_search field which is done to look up a person's records before a transaction (I also thought about using the resetting hitNumber as a transaction separator, but its not always a clean reset per transaction).
My question is, is it possible to group by the fullVisitorId+VisitId, date and this logic where we would have all of the array_agg reset each time the flight_search field is fired? Currently, all the transactional data is in going into one array instead of separate arrays per transaction. Its then impossible to tell which fields go with which transaction. Further, taking the max is supposed to give me the last updates in each transaction, but it just gives me the last transaction because they are all together.
Example of my query below. I have to use array_agg or something like it since the subqueries can only have one return
WITH eventData AS (
SELECT
CONCAT(fullVisitorId, ' ', CAST(VisitId AS string)) sessionId,
date AS date,
hit.hour AS checkinHour,
hit.minute AS checkinMin,
(SELECT ARRAY_AGG(hit.eventInfo.eventAction) FROM UNNEST(hits) hit WHERE hit.eventInfo.eventCategory = 'pnr') AS pnr,
(SELECT ARRAY_AGG(STRUCT(hit.eventInfo.eventAction)) AS val FROM UNNEST(hits) hit WHERE hit.eventInfo.eventCategory = 'submit_checkin') AS names
FROM
`web-analytics.192016109.ga_sessions_20191223`,
UNNEST(hits) AS hit
## group by sessionId, date, hit.eventInfo.eventCategory ='flight_search'
)
SELECT
sessionId,
date,
MAX(checkinHour) chkHr,
MAX(checkinMin) AS chkMin,
# end of transaction
MAX(pnr[ORDINAL(ARRAY_LENGTH(pnr))]) AS pnr,
names.eventAction AS pax_name
FROM
eventData,
UNNEST (names) AS names
GROUP BY
sessionId,
date,
pax_name
Technically if I add a group by here, everything will break because Ill be asked to then group by hour, min and then hits which is an array...
Example test data
This is the original eventData as it is fed in from Google Analytics to BigQuery. I have simplified the displayed eventCategories. This is where the inner query is sourcing. A transaction is completed after the submit_checkin event happens. As we can see though, there is one pnr (identifier) but multiple people are checked-in for that pnr.
This is a sample of the output from eventData looks like. As you can see, the pnrs are grouped in one array and the names are in one array. Its not directly possible to see which were together in which transaction.
Lastly, here is the whole query output. I wrote on the picture what the expected result is.

Answer 1

If you want to see which information was tracked in the same hit you should keep the relation between them. But it seems they are not in the same hit with eventCategory being 'pnr' one time and 'submit_checkin' the other time.
I'm not sure it's intentional but you're also cross joining the table with hits ... and then you're array_agg()-ing the hits array per hit again. That seems wrong.
If you're staying on session scope then there is no need to group anything, because the table already comes with 1 row = 1 session.
This query prepares another window function
SELECT
fullVisitorId,
visitstarttime,
date,
ARRAY(
SELECT AS STRUCT
hitNumber,
IF(eventInfo.eventCategory='flight_search'
AND
LAG(eventInfo.eventCategory) OVER (ORDER BY hitnumber ASC) = 'submit_checkin', 1, 0
) as breakInfo,
eventInfo,
hour,
minute
FROM UNNEST(hits) hit
WHERE hit.eventInfo.eventCategory IN ('pnr', 'submit_checkin', 'flight_search')
ORDER BY hitnumber ASC
) AS myhits1,
ARRAY(SELECT AS STRUCT
*,
SUM(breakInfo) OVER (order by hitnumber) as arrayId
FROM (SELECT
hitNumber,
IF(eventInfo.eventCategory='flight_search'
AND
LAG(eventInfo.eventCategory) OVER (ORDER BY hitnumber ASC) = 'submit_checkin', 1, 0
) as breakInfo,
eventInfo,
hour,
minute
FROM UNNEST(hits) hit
WHERE hit.eventInfo.eventCategory IN ('pnr', 'submit_checkin', 'flight_search')
ORDER BY hitnumber ASC
)) AS myhits2
FROM
`web-analytics.192016109.ga_sessions_20191223`
This gives you a number as id to group by. You only need to feed the output that gets fed to the array function to yet another sub-query that finally groups it into arrays using array_agg() and group by arrrayId.