How can I filter on result of aggregate functions like min, max, sum?

All we need is an easy explanation of the problem, so here it is.

In the below query:

SELECT user_id, (max(ts) -  min(ts)) as tsdiff
               FROM analytics 
               GROUP BY user_id

How can I filter on on tsdiff which I assume is a interval? For example I’d like to filter for all records where tsdiff is larger than 1d (one day).

Even if I were to use a subquery, I’d face the same issue again.

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

Use a HAVING clause:

SELECT 
  user_id
 ,(max(ts) -  min(ts)) as tsdiff
FROM 
  analytics 
GROUP BY 
  user_id
HAVING
  max(ts) -  min(ts) > interval '1 day'

See:
https://www.postgresql.org/docs/current/tutorial-agg.html

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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