Cool Stuff in Snowflake – Part 10: RATIO_TO_REPORT

I’m doing a little series on some of the nice features/capabilities in Snowflake (the cloud data warehouse). In each part, I’ll highlight something that I think it’s interesting enough to share. It might be some SQL function that I’d really like to be in SQL Server, it might be something else.

This episode talks about a new window function Snowflake recently introduced: RATIO_TO_REPORT. The function returns the ratio of the value of the current row to the sum of the values within the set. Or in other words, some sort of “percentage of total”. Nothing we couldn’t calculate before, but a bit of syntactic sugar so we don’t have to write two expressions.

An example using the StackOverflow database:

WITH CTE_SourceData AS
(
SELECT
     MONTH(p.POSTCREATIONDATE)  AS MonthNbr
    ,pt.POSTTYPEDESC
    ,COUNT(p.POSTID)            AS Cnt 
FROM STACKOVERFLOW.DBO.POSTS    p
JOIN STACKOVERFLOW.DBO.POSTTYPE pt ON p.POSTTYPEID = pt.POSTTYPEID
WHERE YEAR(p.POSTCREATIONDATE) = 2018
GROUP BY pt.POSTTYPEDESC,MonthNbr
)
SELECT
     MonthNbr
    ,PostTypeDesc
    ,Cnt
    ,RATIO_TO_REPORT(Cnt) OVER (PARTITION BY MonthNbr) AS PctOfTotal
FROM CTE_SourceData
ORDER BY MonthNbr, PctOfTotal DESC;

The query calculates the percentage of total of the different post types for each month. This gives the following result:

If you’re wondering, here’s how we would originally write the SQL expression (in SQL Server for example):

If you’re in the area of Mechelen, Belgium at the 8th of October 2019, you can catch me talking about Snowflake at DataMinds Connect. If you’re interested, drop by and say hi!