SQL - count value breaks in a column when specifying break parameters - sql

Question

This builds on a previous question of mine here.
I have a table which tracks service involvement (srvc_invl) for two individuals (name) over a period of time (day).
name day srvc_inv
Liam 1 1
Liam 2 0
Liam 3 1
Liam 4 0
Liam 5 0
Liam 6 1
Liam 7 0
Noel 1 0
Noel 2 0
Noel 3 1
Noel 4 0
Noel 5 1
Noel 6 1
Noel 7 1
My goal is to count the number of unique service involvements per individual. Previously, we accomplished this by counting breaks in service involvement 1's and 0's using a lag function:
select name, count(*)
from (select t.*,
lag(srvc_inv, 1, 0) over (partition by name order by day) as prev_srvc_inv
from t
) t
where prev_srvc_inv = 0 and srvc_inv = 1
group by name;
However, I have just found out that breaks in service involvement can be defined differently based on the program of interest. I.e. for some programs, one-day of non-consecutive service counts as a break, for example:
day srvc_inv
1 1
2 0
3 1
= 2 service episodes
but for other programs, two or more days of non-consecutive service counts as a break, for example:
day srvc_inv
1 1
2 0
3 1
= 1 service episode, but
day srvc_inv
1 1
2 0
3 0
4 1
5 0
= 2 service episodes
Using the table at the top of this post, let us assume we are analyzing a program that considers two days of non-consecutive service involvement to be a service break and thus a distinct service episode.
How would I modify the above query, or write a new query, that would allow me to specify the break number parameters?
My desired output is as follows:
name srvc_episodes
Liam 2
Noel 1
Thank you so so so much for any help anyone can offer on this!

Answer 1

Use a running sum rather than lag(). This gives you more flexibility:
select name, count(*)
from (select t.*,
sum(srvc_inc) over (partition by name
order by day
rows between 2 preceding and 1 preceding
) as sum_srvc_inc_2
from t
) t
where (sum_srvc_inc_2 = 0 or sum_srvc_inc_2 is null) and srvc_inc = 1
group by name;
You would adjust the "2"s for the length of time for the split.

Answer 2

Try this:
SELECT NAME,
SUM(CASE WHEN SRVC_INV = 1
AND (LAG1 = 1 OR LAG2 = 1 OR (LAG1 IS NULL AND LAG2 IS NULL))
THEN 1
ELSE 0
END) AS SERVICE_EPISODES
FROM
(SELECT NAME, SRVC_INV,
LAG(SRVC_INV,1) OVER (PARTITION BY NAME ORDER BY DAY) AS LAG1,
LAG(SRVC_INV,2) OVER (PARTITION BY NAME ORDER BY DAY) AS LAG2
FROM T)
GROUP BY NAME
Cheers!!