I have a list of activities(A-start to H-end) for certain events. These can occur in any order, any number of times and can restart as well. I need to identify the blocks of activities within an event.
Eg: A B C D E F G H B C D H C D E F H E F G H
It starts only once (A) but ends multiple times
Need to number these activities to identify sets (How many times it ended)
output: 1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 3 4 4 4 4 5
This helps me identify that the event ended (H) 5-1 = 4 times
If your events are series of events in time - try to play with the MATCH() clause and its dependent functions event_name(), pattern_id() and match_id() .
I just created a timeseries out of your input letters, spaced by one-hour intervals, and applied a MATCH() clause. If the PATTERN pat AS () clause uncannily reminds you of a grep expression, that's the way it works.
Just look at the query's output - and imagine how many interesting things you could do with the pattern_id-s and the match_id-s that you get- grouping by them, for example, in subsequent SELECT-s ...
WITH
s(tm,event) AS (
SELECT TIME '00:00:00','A'
UNION ALL SELECT TIME '01:00:00','B'
UNION ALL SELECT TIME '02:00:00','C'
UNION ALL SELECT TIME '03:00:00','D'
UNION ALL SELECT TIME '04:00:00','E'
UNION ALL SELECT TIME '05:00:00','F'
UNION ALL SELECT TIME '06:00:00','G'
UNION ALL SELECT TIME '07:00:00','H'
UNION ALL SELECT TIME '08:00:00','B'
UNION ALL SELECT TIME '09:00:00','C'
UNION ALL SELECT TIME '10:00:00','D'
UNION ALL SELECT TIME '11:00:00','H'
UNION ALL SELECT TIME '12:00:00','C'
UNION ALL SELECT TIME '13:00:00','D'
UNION ALL SELECT TIME '14:00:00','E'
UNION ALL SELECT TIME '15:00:00','F'
UNION ALL SELECT TIME '16:00:00','H'
UNION ALL SELECT TIME '17:00:00','E'
UNION ALL SELECT TIME '18:00:00','F'
UNION ALL SELECT TIME '19:00:00','G'
UNION ALL SELECT TIME '20:00:00','H'
)
SELECT
*
, event_name()
, pattern_id()
, match_id()
FROM s
MATCH(
PARTITION BY 1 -- nothing to partition by
ORDER BY tm
DEFINE
START_ev AS (event='A')
, any_ev AS (event NOT IN ('A','H'))
, END_ev AS (event='H')
PATTERN pat AS (start_ev* any_ev+ end_ev)
ROWS MATCH FIRST EVENT
);
tm |event|event_name|pattern_id|match_id
00:00:00|A |START_ev | 1| 1
01:00:00|B |any_ev | 1| 2
02:00:00|C |any_ev | 1| 3
03:00:00|D |any_ev | 1| 4
04:00:00|E |any_ev | 1| 5
05:00:00|F |any_ev | 1| 6
06:00:00|G |any_ev | 1| 7
07:00:00|H |END_ev | 1| 8
08:00:00|B |any_ev | 2| 1
09:00:00|C |any_ev | 2| 2
10:00:00|D |any_ev | 2| 3
11:00:00|H |END_ev | 2| 4
12:00:00|C |any_ev | 3| 1
13:00:00|D |any_ev | 3| 2
14:00:00|E |any_ev | 3| 3
15:00:00|F |any_ev | 3| 4
16:00:00|H |END_ev | 3| 5
17:00:00|E |any_ev | 4| 1
18:00:00|F |any_ev | 4| 2
19:00:00|G |any_ev | 4| 3
20:00:00|H |END_ev | 4| 4
MATCH() clause is optimized appropriately.
It looks like you want to count the number of "H"s and "A"s before a given value. This requires having a column that specifies the ordering. Let me assume this column is called id.
Then, you can do this with window functions:
select t.*,
sum(case when col = 'H' then 1 else 0 end) over (partition by grp order by id) + 1 as output
from (select t.*,
sum(case when col = 'A' then 1 else 0 end) over (order by id) as grp
from t
) t;
The subquery defines the "activity" groups, by doing a cumulative sum of "A"s. The outer query then defines the "event" groups by doing a cumulative sum of "E"s.
To be honest, I cannot tell if the "H" is part of the preceding value or the next value. If the next value then the query can use a window clause or a slight tweak to the logic:
(sum(case when col = 'H' then 1 else 0 end) over (partition by grp order by id) +
(case when col = 'H' then 0 else 1 end)
) as output
