I find GQL in GCP very limited in functionality and inconvenient. I've spent quite a bit of time to find the equivalent of this simple SQL query in GQL to no avail:
SELECT COUNT(*) FROM Account WHERE accountToken IS NOT null
Any suggestions as how to go about this would be much appreciated.
You can use the "Datastore Statistics" tab (the link right under the Datastore Viewer), choose "Display Statistics for: (your entity type)" and it will show you the total number of entities; however, this is not the freshest view of the data (updated "at least once per day").
Here you can read more about Datastore Statistics.