Building a monthly Snapshot VIEW from historical data - sql

Question

I have historical historical data that looks as following:
I need to get a DB VIEW of how each of these Opportunities looked like at the end of the month e.g.
What is the best way to implement this as a Snowflake VIEW?

Answer 1

Well there are two parts, the SQL that goes in the view, and the view to use.
The SQL appears to be the "last value of the month" per opportunity AND deleted is not true, which can be done a couple of ways.
Off the top of my head the most recent value of the month sounds like WHERE clause like against ROW_NUMBER:
SELECT last_modified_date,
opportunity,
amount
FROM table
WHERE deleted == false
AND ROW_NUMBER() OVER(PARTITON BY date_trunc('month', last_modified_date) ORDER BY last_modified_date DESC) = 1
This will keep the values you want, then we need to tweak the last_modified_date to the last day of the month, which can be done via
SELECT dateadd('day', -1 ,dateadd('month', 1, date_trunc('month', last_modified_date))) as month_end
which can be combined as:
SELECT dateadd('day', -1 ,dateadd('month', 1, date_trunced)) as month_end,
opportunity,
amount
FROM (
SELECT
date_trunc('month', last_modified_date) AS date_trunced
opportunity,
amount,
ROW_NUMBER() OVER(PARTITON BY date_trunced ORDER BY last_modified_date DESC) AS rn
FROM table
WHERE deleted == false
)
WHERE rn = 1
ORDER BY 1,2;
Then is you have a few million rows, you could just create a normal view, BUT if you have billions of rows, and years of data, the prior months are going to be rather gross churn over, so a materialized view would be helpful, but I am rather sure you cannot use a ROW_NUMBER in a materialized view, thus you could manually build a "historic months" table, and "current months" view, and union those together, and on some period like month roll the current periods data into history as that becomes stable.