Bigquery/ SQL: sequence in same group

Question

I have a question in regards to finding the sequence between 2 page types using sql:

Sample data we have:

SessionID	Page Type
123	account
123	raw
123	plp
123	pdp
123	account
123	plp
123	sample
123	pdp
123	plp
123	pdp
123	raw

Ideally output will look like below, only to include records when pdp is clicked right after plp

SessionID	Page Type
123	plp
123	pdp
123	plp
123	pdp

Answer 1

In order to operate based on order - you must have something to order on
Usually it is timestamp column or position or something else

I assume you have one (in my sample I will use ts column as such)

Consider below approach to get what you want

select * from your_table
qualify (lag(page_type) over win = 'plp' and page_type = 'pdp')
or (lead(page_type) over win = 'pdp' and page_type = 'plp')
window win as (partition by sessionId order by ts)

with output