How can i find rows before a specific value? - sql

Question

I have the next row and what I want to do is to select all the rows before the type "shop". I tried using case in the "where clause" but I didn't get any result. How can I do it?
|id|visitnumber|type |
|01| 1|register|
|01| 2|visit |
|01| 3|visit |
|01| 4|shop |
|01| 5|visit |
For example, what I want to get is the visitnumber before type = "shop".
it would be very helpful because what I'm trying to do is to get all the actions that happened before an specific event on big query.
|id|numberofvisits|
|01| 3|

Answer 1

One method uses correlated subqueries:
select id, count(*)
from t
where visitnumber < (select min(t2.visitnumber) from t t2 where t2.id = t.id and type = 'shop')
group by id;
However, in BigQuery, I prefer an approach using window functions:
select id, countif(visitnumber < visitnumber_shop)
from (select t.*,
min(case when type = 'shop' then visitnumber end) over (partition by id) as visitnumber_shop
from t
) t
group by id;
This has the advantage of keeping all ids even those that don't have a "shop" type.

Answer 2

One option uses a subquery for filtering:
select id, count(*) number_of_visits
from mytable t
where t.visit_number < (
select min(t1.visit_number)
from mytable t
where t1.id = t.id and t1.type = 'shop'
)
group by id
You can also use window functions:
select id, count(*) number_of_visits
from (
select
t.*,
countif(type = 'shop') over(partition by id order by visit_number) has_shop
from mytable t
) t
where has_shop = 0
group by id

Answer 3

Below option is for BigQuery Standard SQL
#standardSQL
SELECT id,
ARRAY_LENGTH(SPLIT(REGEXP_EXTRACT(',' || STRING_AGG(type ORDER BY visitnumber), r'(.*?),shop'))) - 1 AS number_of_visits_before_first_shop
FROM `project.dataset.table`
GROUP BY id
You can test, play with above using dummy data as in below example
#standardSQL
WITH `project.dataset.table` AS (
SELECT '01' id, 1 visitnumber, 'register' type UNION ALL
SELECT '01', 2, 'visit' UNION ALL
SELECT '01', 3, 'visit' UNION ALL
SELECT '01', 4, 'shop' UNION ALL
SELECT '01', 5, 'visit' UNION ALL
SELECT '02', 1, 'register' UNION ALL
SELECT '02', 2, 'visit' UNION ALL
SELECT '02', 3, 'visit' UNION ALL
SELECT '03', 1, 'shop' UNION ALL
SELECT '03', 2, 'shop' UNION ALL
SELECT '03', 3, 'visit'
)
SELECT id,
ARRAY_LENGTH(SPLIT(REGEXP_EXTRACT(',' || STRING_AGG(type ORDER BY visitnumber), r'(.*?),shop'))) - 1 AS number_of_visits_before_first_shop
FROM `project.dataset.table`
GROUP BY id
with result
Row id number_of_visits_before_first_shop
1 01 3
2 02 null
3 03 0

Answer 4

This is the query i run on Big Query with an Analytics 360 test dataset:
select
id,
visitnumber,
countif(hit_number < hitnumber_quickviewclick) as hitsprev_quickviewclick
from (
select
a.fullVisitorID as id,
a.visitnumber as visitnumber,
h.hitNumber as hit_number,
MIN (case when h.eventInfo.eventAction = 'Quickview Click' then h.hitNumber end) over (partition by a.fullVisitorID) as hitnumber_quickviewclick
FROM `bigquery-public-data.google_analytics_sample.ga_sessions_20170725` as a
CROSS JOIN UNNEST(hits) as h
) as T
group by 1,2;
I wanted to make a query where i could find the total number of hits before the event action 'quickview click' hitted. If this is wrong or can be improved let me know!
Thanks a lot, guys!

Answer 5

This is how I would approach in SQL in general:
select count(*)
from yourtable yt
where type = 'visit' and not exists (
select 1
from yourtable yt2
where yt.id > yt2.id and yt2.type = 'shop'
)
However, I would very much think about situations when we want to find visits before the next shop... And the next shop... And the next shop. For that purpose you could find out the ids of shop and group by intervals.