Postgresql - calculate field has_impact based on start and end time

zealous
June 13, 2023
158 views
0 votes
2 Answers

Trying to populate field has_impact based on the following for each feed view in the session.

has_impact is true when difference between (view_end_time – view_start_time) > 3 and view_perc > 0.8 else false.

view_logs table

create table view_logs(session_id varchar(10), post_id int, 
                         ts int, event_name varchar(50), view_perc float);
    
insert into view_logs(session_id, post_id, ts, event_name, view_perc)
    values
    ('m1', 1000, 1524600, 'view_start', null),
    ('m1', 1000, 1524602, 'view_end', 0.85),
    ('m1', 1000, 1524650, 'view_start', null),
    ('m1', 1000, 1524654, 'view_end', 0.9),
    ('m1', 2000, 1524700, 'view_start', null),
    ('m1', 2000, 1524707, 'view_end', 0.3),
    ('m1', 2000, 1524710, 'view_start', null),
    ('m1', 2000, 1524713, 'view_end', 0.9);

I have tried this fiddle but not getting desired output. can anyone help me to identify what I am doing wrong?

query:

with cte as
  (  
    select
      pv1.session_id,
      pv1.post_id,
      pv2.view_perc,
      pv1.ts as start_time,
      min(pv2.ts) as end_time
    from view_logs pv1
    join view_logs pv2
    on pv1.session_id = pv2.session_id
    and pv1.post_id = pv2.post_id
    and pv1.event_name <> pv2.event_name
    and pv1.ts < pv2.ts
    group by
      pv1.session_id,
      pv1.post_id,
      pv2.view_perc,
      pv1.ts
 )  
 
select
    session_id,
    post_id,
    start_time,
    end_time,
    case
        when (end_time - start_time > 3  and view_perc > 0.8 )then 'yes'
        else 'no'
    end as has_meaningful_view
from cte

desired output:

*--------------------------------------------------------*
|session_id| post_id | start_time | end_time | has_impact|
*--------------------------------------------------------*
|  m1      | 1000    | 1524600    | 1524602  | no        |
|  m1      | 1000    | 1524650    | 1524654  | yes       |
|  m1      | 2000    | 1524700    | 1524707  | no        |
|  m1      | 2000    | 1524710    | 1524714  | no        |
*--------------------------------------------------------*

Tags: postgresql sql

Answers

this might not get you exactly what you want but it does calculate the has_impact column

WITH cte
AS (
    SELECT *
        ,CASE 
            WHEN event_name = 'view_start'
                THEN ts
            END AS start_time
        ,CASE 
            WHEN event_name = 'view_end'
                THEN ts
            END AS end_time
    FROM view_logs
    )
SELECT session_id
    ,post_id
    ,start_time
    ,end_time
    ,CASE 
        WHEN end_time - lag(start_time, 1) OVER (
                ORDER BY (
                        SELECT NULL
                        )
                ) > 3
            AND view_perc > 0.8
            THEN true
        ELSE false
        END AS has_impact
FROM cte;

output:

session_id	post_id	start_time	end_time	has_impact
m1	1000	1524600	null	false
m1	1000	null	1524602	false
m1	1000	1524650	null	false
m1	1000	null	1524654	true
m1	2000	1524700	null	false
m1	2000	null	1524707	false
m1	2000	1524710	null	false
m1	2000	null	1524713	false

Supposing that each start time has an end time, you can aggregate using row_number function as the following:

select session_id, post_id,
       max(case when event_name='view_start' then ts end) startTime,
       max(case when event_name='view_end' then ts end) endTime,
       case 
         when 
          max(case when event_name='view_end' then ts end)
        - max(case when event_name='view_start' then ts end) > 3 
          and max(view_perc) > 0.8
         then 'yes' else 'no'
       end as hasimpact
from
(
  select *,
    row_number() over (partition by session_id, post_id order by ts) rn
  from view_logs
) t
group by session_id, post_id, (rn-1)/ 2
order by session_id, post_id, min(ts)

Demo

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Postgresql – calculate field has_impact based on start and end time

Answers