How to calculate the "average engagement time" of GA4 using Big Query?

Question

I need to create a "session level" table using big query. For this, I use the session_id, user_speudo_id and other metrics/dimensions. When I try to calculate the "average engagement time" of GA4, I use the following formula.

However, I get 19 minutes with BigQuery while GA4 shows an average engagement time of 30 minutes. Has anyone ever calculated this metric with BigQuery?

SELECT
    DISTINCT ( SELECT value.int_value FROM UNNEST(event_params) WHERE key = 'ga_session_id') AS session_id,
    max((select value.int_value from unnest(event_params) where key = 'engagement_time_msec')) as timeOnSite_ms 
FROM tableXXXX 

Answer 1

try this one

SELECT 

distinct (SELECT value.int_value FROM UNNEST(event_params) WHERE key = 'ga_session_id')  AS session_id,
sum((select value.int_value from unnest(event_params) where key = 'engagement_time_msec'))/1000 as timeOnSite_sec


FROM table_xxx

group by session_id