Note: Before you move forward, make sure that you have connected your GA4 property with a BigQuery project. If you haven’t then check out this article first: GA4 BigQuery – Connect Google Analytics 4 with BigQuery
Introduction to custom GA4 schema
When you send data from a GA4 property to BigQuery, you use the default schema (i.e. structure) provided by Google.
As a result, Google automatically created a set of tables (‘events_‘ and ‘events_intraday_‘) in the pre-built dataset (“analytics_<property_id>“).
You do not get the option of creating the data tables you want or setting the fields you want to see in the data table(s):
When you use the default schema you have no control over the fields (columns) that appear in your data tables and no control over the number and type of data tables you see in your dataset.
If you want to see your data tables with only the fields you want, then you need to first create your own schema (also called Custom Schema).
The custom schema that you create depends on the data source being used.
For example, if you are using GA4 as a data source, then you define a schema by selecting the dimensions and metrics you want to see in your data table.
Then you add one or more queries to it.
The GA4 data that you send to BigQuery via custom schema is called the custom GA4 data.
How to send custom GA4 data to BigQuery
Following is the 10,000 foot view of sending custom GA4 data to BigQuery: