Find average number of views before first lead event happens - sql

Question

create table events (
fk_user integer,
event varchar(40),
time integer
);
Insert into events (fk_user, event, time)
VALUES
('1', 'view', '1'),
('1', 'view', '3'),
('1', 'view', '4'),
('1', 'lead', '5'),
('1', 'view', '6'),
('1', 'view', '7'),
('1', 'lead', '9'),
('2', 'view', '1'),
('2', 'lead', '2'),
('2', 'lead', '3'),
('2', 'view', '6'),
('2', 'view', '7'),
('2', 'view', '8'),
('5', 'view', '1'),
('5', 'view', '2'),
('2', 'view', '4'),
('2', 'lead', '5'),
('2', 'view', '9');
What I am trying to find is: There are 3 'views' before a 'lead' occurs from the top. I want to take the average of the 'time' of first three occurrences. Is it possible to do with the window function ?
Expected output should be: (1+3+4)/3 = 2.666 (If taken integer then 3)

Answer 1

You can use the min window function along with a case statement to find the first_lead_time per fkuser and then use a derived table to get the average value of the views rows that become before the first_lead_time
select fkuser, avg(time) from (
select * ,
min (case when event = 'lead' then time end) over (partition by fkuser) as first_lead_time
from events
) t where time < first_lead_time
and event = 'view'
group by fkuser
Another way
select e.fk_user, avg(e.time)
from events e
join (
select min(time) first_lead_time, fkuser
from events
where event = 'lead'
group by fkuser
) t on t.fkuser = e.fkuser
where e.time < t.first_lead_time
group by e.fkuser