Can I put a condition on a window function in Redshift? - sql

Question

I have an events-based table in Redshift. I want to tie all events to the FIRST event in the series, provided that event was in the N-hours preceding this event.
If all I cared about was the very first row, I'd simply do:
SELECT
event_time
,first_value(event_time)
OVER (ORDER BY event_time rows unbounded preceding) as first_time
FROM
my_table
But because I only want to tie this to the first event in the past N-hours, I want something like:
SELECT
event_time
,first_value(event_time)
OVER (ORDER BY event_time rows between [N-hours ago] and current row) as first_time
FROM
my_table
A little background on my table. It's user actions, so effectively a user jumps on, performs 1-100 actions, and then leaves. Most users are 1-10x per day. Sessions rarely last over an hour, so I could set N=1.
If I just set a PARTITION BY date_trunc('hour', event_time), I'll double create for sessions that span the hour.
Assume my_table looks like
id | user_id | event_time
----------------------------------
1 | 123 | 2015-01-01 01:00:00
2 | 123 | 2015-01-01 01:15:00
3 | 123 | 2015-01-01 02:05:00
4 | 123 | 2015-01-01 13:10:00
5 | 123 | 2015-01-01 13:20:00
6 | 123 | 2015-01-01 13:30:00
My goal is to get a result that looks like
id | parent_id | user_id | event_time
----------------------------------
1 | 1 | 123 | 2015-01-01 01:00:00
2 | 1 | 123 | 2015-01-01 01:15:00
3 | 1 | 123 | 2015-01-01 02:05:00
4 | 4 | 123 | 2015-01-01 13:10:00
5 | 4 | 123 | 2015-01-01 13:20:00
6 | 4 | 123 | 2015-01-01 13:30:00

Answer 1

The answer appears to be "no" as of now.
There is a functionality in SQL Server of using RANGE instead of ROWS in the frame. This allows the query to compare values to the current row's value.
https://www.simple-talk.com/sql/learn-sql-server/window-functions-in-sql-server-part-2-the-frame/
When I attempt this syntax in Redshift I get the error that "Range is not yet supported"
Someone update this when that "yet" changes!