Matching BigQuery data with Traffic Acquisition GA4 report

Question

I'm new to BigQuery and I'm trying to replicate the Traffic Acquisition GA4 report, but not very successfully at the moment, as my results are not even remotely close to the GA4 view.

1. I understand that the source/medium/campaign fields are event-based and not session-based in GA4 / BQ. My question is, why not every event has a source/medium/campaign as an event_parameter_key? It seems logical for me to have these parameters for the 'session_start' event, but unfortunately, it's not the case

2. I tried the following options to replicate the Traffic Acquisition report:

2.1 To check the first medium for sessions:

with cte as ( select
    PARSE_DATE("%Y%m%d", event_date) AS Date,
    user_pseudo_id,
    concat(user_pseudo_id,(select value.int_value from unnest(event_params) where key = 'ga_session_id')) as session_id,
    FIRST_VALUE((select value.string_value from unnest(event_params) where key = 'medium')) OVER (PARTITION BY concat(user_pseudo_id,(select value.int_value from unnest(event_params) where key = 'ga_session_id')) ORDER BY event_timestamp) as first_medium

FROM `project`)

select Date, first_medium, count(distinct user_pseudo_id) as Users, count (distinct session_id) as Sessions
from cte
group by 1,2;

The query returns 44k users with 'null' medium and 1.8k organic users while there are 17k users with the 'none' medium and 8k organic users in GA4.

2.2 If I change the first medium to the last medium:

FIRST_VALUE((select value.string_value from unnest(event_params) where key = 'medium')) OVER (PARTITION BY concat(user_pseudo_id,(select value.int_value from unnest(event_params) where key = 'ga_session_id')) ORDER BY event_timestamp desc) as last_medium

Organic medium increases to 9k users, though the results are still not matching the GA4 data.

2.3 I've also tried this code - https://www.ga4bigquery.com/traffic-source-dimensions-metrics-ga4/ - source / medium (based on session) , and still got completely different results compared to the GA4.

Any help would be much appreciated!

Answer 1

I have noticed the samething, looking deeper I pulled 1 days worth of data from big query into google sheets and examined it.

Unsurprisingly I could replicate the results from ga4bigquery codes you have mentioned above results but they did not align with GA4 and although close for high traffic pages could be wildly out for the lower ones.

I then did a count for 'email' in event parmas source & ea_tracking_id as well as traffic_source and found they are all lower than the GA4 analytics.

I went to my dev site where I know exactly how many sessions have a source of email GA4 analytics agreed but big query did not, Google seems to be allocating a some traffic to not set randomly.

I have concluded the problem is not in the SQL and not in the tagging but in the bigquery GA4 data source. I have logged a query with google and we will see what happens. Sorry its not a solution