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

Assuming SETTLEMENTDATE is of DATE data type, you can use below to get today's partition

SELECT *
FROM `biengine-252003.aemo2.daily`
WHERE SETTLEMENTDATE = CURRENT_DATE()     

or, for example for yesterday's partition

SELECT *
FROM `biengine-252003.aemo2.daily`
WHERE SETTLEMENTDATE = DATE_SUB(CURRENT_DATE(), INTERVAL 1 DAY)     

See more at https://cloud.google.com/bigquery/docs/querying-partitioned-tables#querying_partitioned_tables_2

Answer 2

Now that scripting is in beta in BigQuery, you can declare a variable that contains the target date. Here's an example:

SET max_date DATE DEFAULT (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'

Answer 3

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.