If you’ve ever tried to build a channel report in BigQuery and thought traffic_source.source would magically solve everything - bad news. And if you assumed default_channel_grouping was available too - more bad news.
There’s no such field in GA4 BigQuery.
If you want channel groupings like you see in the GA4 interface, you’ll have to build them yourself. Manually. With CASE WHEN. Preferably without tears.
Why is it like this?
Because GA4 is event-based. Channel info is captured either:
• at the first visit (via traffic_source.*), or
• from UTM parameters inside event_params, session_source fields or collected_traffic_source fields.
And from there on, it’s up to you to decide which one to trust. BigQuery won’t help - you’re on your own.
What are your options?
1. The lazy route: just use session_traffic_source_last_click.
But then “facebook / cpc” and “instagram / paid_social” will end up in different universes.
2. The proper way: create your own Channel Grouping using CASE WHEN. For example:
• source = 'google' AND medium = 'cpc' → 'Paid Search'
• medium = 'organic' → 'Organic Search'
• source CONTAINS 'facebook' → 'Paid Social'
• ...and so on
Sounds simple? It is - until you try covering the full zoo of UTM values your 12 agencies, internal teams, and push notifications (with utm_medium = awesomeness) come up with.
Why bother?
• To compare channel performance the way you want, not how GA4’s UI decides.
• To clean up the mess of 100,000+ unique source/medium combos that happen when every manager makes up their own naming conventions.
• To finally get a clear answer to: “How much revenue did Paid Social really bring in?”
Takeaway:
GA4 BigQuery isn’t a magical table. It’s raw data. And CASE WHEN is your tool to turn that chaos into a clean, reliable report.
A bit of patience, a little logic—and you’ll have a Channel Grouping that rivals GA4’s interface. Except now it’s fully yours. And under your control.
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