create table sess (student Int64, events String, session_is_new Int8, session_number Int64 ) Engine=Log;
insert into sess values (1, 'ev1', 1, 1),  (1, 'ev2', 0, 1),  (1, 'ev3', 0, 1),  (1, 'ev4', 1, 2);
insert into sess values (2, 'ev1', 1, 1);

SELECT student, sum(session_is_new) OVER (PARTITION BY student)  session_number
from  sess

┌─student─┬─x─┐
│       1 │ 1 │
│       1 │ 1 │
│       1 │ 1 │
│       1 │ 2 │
└─────────┴───┘
┌─student─┬─x─┐
│       2 │ 1 │
└─────────┴───┘

select student, arrayJoin(arrayZip(x,y))
from (
SELECT student, arrayCumSum(groupArray(session_is_new)) x, groupArray(session_number) y
from  sess
group by student)

┌─student─┬─arrayJoin(arrayZip(x, y))─┐
│       2 │ (1,1)                     │
│       1 │ (1,1)                     │
│       1 │ (1,1)                     │
│       1 │ (1,1)                     │
│       1 │ (2,2)                     │
└─────────┴───────────────────────────┘

select student, session_is_new, sess_num, session_number, events
from (
SELECT student, arrayCumSum((groupArray( (session_is_new, session_number, events) ) as g).1) gsess_num, g.1 as gsession_is_new, g.2 as gsession_number, g.3 as gevents
from  sess
group by student
) array join gsess_num as sess_num, gsession_is_new as session_is_new,gsession_number as session_number, gevents as events
order by student, events

┌─student─┬─session_is_new─┬─sess_num─┬─session_number─┬─events─┐
│       1 │              1 │        1 │              1 │ ev1    │
│       1 │              0 │        1 │              1 │ ev2    │
│       1 │              0 │        1 │              1 │ ev3    │
│       1 │              1 │        2 │              2 │ ev4    │
│       2 │              1 │        1 │              1 │ ev1    │
└─────────┴────────────────┴──────────┴────────────────┴────────┘

cat your_sql_file.sql | clickhouse-client --receive_timeout=3600 --idle_timeout=3600 -mn --echo --progress