BigQuery filter per the last Date and use Partition

Question

I asked how to filter the last date and got excellent answers (BigQuery, how to use alias in where clause?), they all work, but, they scan the whole table, the field SETTLEMENT

Answer 1

Mikhail's answer looks like this (working on public data):

SELECT MAX(views)
FROM `fh-bigquery.wikipedia_v3.pageviews_2019` 
WHERE DATE(datehour) = DATE_SUB(CURRENT_DATE(), INTERVAL 7 DAY)     
AND wiki='es' 
# 122.2 MB processed

But it seems the question wants something like this:

SELECT MAX(views)
FROM `fh-bigquery.wikipedia_v3.pageviews_2019` 
WHERE DATE(datehour) = (SELECT DATE(MAX(datehour)) FROM `fh-bigquery.wikipedia_v3.pageviews_2019` WHERE wiki='es')     
AND wiki='es'
# 50.6 GB processed

... but for way less than 50.6GB

What you need now is some sort of scripting, to perform this in 2 steps:

max_date = (SELECT DATE(MAX(datehour)) FROM `fh-bigquery.wikipedia_v3.pageviews_2019` WHERE wiki='es')   

;

SELECT MAX(views)
FROM `fh-bigquery.wikipedia_v3.pageviews_2019` 
WHERE DATE(datehour) = {{max_date}}
AND wiki='es'
# 115.2 MB processed

You will have to script this outside BigQuery - or wait for news on https://issuetracker.google.com/issues/36955074.