How to partition by a customized sum value? - sql

Question

I have a table with the following columns: customer_id, event_date_time
I'd like to figure out how many times a customer triggers an event every 12 hours from the start of an event. In other words, aggregate the time between events for up to 12 hours by customer.
For example, if a customer triggers an event (in order) at noon, 1:30pm, 5pm, 2am, and 3pm, I would want to return the noon, 2am, and 3pm record.
I've written this query:
select
cust_id,
event_datetime,
nvl(24*(event_datetime - lag(event_datetime) over (partition BY cust_id ORDER BY event_datetime)),0) as difference
from
tbl
I feel like I'm close with this. Is there a way to add something like
over (partition BY cust_id, sum(difference)<12 ORDER BY event_datetime)
EDIT: I'm adding some sample data:
+---------+-----------------+-------------+---+
| cust_id | event_datetime | DIFFERENCE | X |
+---------+-----------------+-------------+---+
| 1 | 6/20/2015 23:35 | 0 | x |
| 1 | 6/21/2015 0:09 | 0.558611111 | |
| 1 | 6/21/2015 0:49 | 0.667777778 | |
| 1 | 6/21/2015 1:30 | 0.688333333 | |
| 1 | 6/21/2015 9:38 | 8.133055556 | |
| 1 | 6/21/2015 10:09 | 0.511111111 | |
| 1 | 6/21/2015 10:45 | 0.600555556 | |
| 1 | 6/21/2015 11:09 | 0.411111111 | |
| 1 | 6/21/2015 11:32 | 0.381666667 | |
| 1 | 6/21/2015 11:55 | 0.385 | x |
| 1 | 6/21/2015 12:18 | 0.383055556 | |
| 1 | 6/21/2015 12:23 | 0.074444444 | |
| 1 | 6/22/2015 10:01 | 21.63527778 | x |
| 1 | 6/22/2015 10:24 | 0.380555556 | |
| 1 | 6/22/2015 10:46 | 0.373611111 | |
+---------+-----------------+-------------+---+
The "x" are the records that should be pulled since they're the first records in the 12 hour block.

Answer 1

If I understand correctly, you want the first record in each 12-hour block where the blocks of time are defined by the first event time.
If so, you need to modify your query to get the difference from the *first * time for each customer. The rest is just arithmetic. The query would look something like this:
with t as (
select cust_id, event_datetime,
(24 * (event_datetime -
coalesce(min(event_datetime) over (partition by cust_id ), 0)
) as difference
from tbl
)
select t.*
from (select t.*,
row_number() over (partition by cust_id, floor(difference / 12)
order by difference) as seqnum
from t
) t
where seqnum = 1;