BigQuery join on closest date match

Question

I'm trying to join two tables in BigQuery based on an id and the closest date match.

Transaction Table:

transactionId	dateTime	productId
4a50665e	2022-05-13T14:12:55	abc
7d5889cd	2022-05-22T16:10:21	abc

Product Log Table (log of when each productId is updated to a new version):

dateTime	productId	version
2022-05-19T06:37:24	abc	v2
2022-05-12T04:38:23	xyz	v1
2022-05-10T09:57:54	abc	v1

I want to add a version column to the transaction table by looking up from the product log table, based on productId match and the dateTime match from the product table. To get the active product version at the time of the transaction.

Desired Result:

transactionId	dateTime	productId	version
4a50665e	2022-05-13T14:12:55	abc	v1
7d5889cd	2022-05-22T16:10:21	abc	v2

Something like this

SELECT
  t.*,
  p.version
FROM
  transaction_table t
LEFT JOIN
  product_log_table p
ON
  t.productId = p.productId AND 
  t.datetime < p.dateTime

But that doesn't work. I've tried searching a lot and tried a number of solutions but can't get anything to work. Should be simple? How do I do this?

Thanks for any help.

Answer 1

Consider below approach

select any_value(t).*, 
  string_agg(version, '' order by p.dateTime desc limit 1) as version
from Transaction_Table t
join Product_Log_Table p
on t.productId = p.productId
and t.dateTime >= p.dateTime 
group by format('%t', t)                  

if applied to sample data in your question - output is