Redash and Dynamodb - GROUP BY using DQL

I’m trying to obtain a count of items in a Dynamodb table - I can run this query fine

scan user_Id from myUploads

but if I run

scan user_Id from myUploads GROUP BY user_Id

I get an error:
Error running query: Error parsing query at line 1

Is this related to Redash, DQL or Dynamo? Where is the best place to learn about DQL examples?

Ultimate goal:
ultimately I’d like a table that counts entries for unique values of user_Id e.g.

1 13
2 8
3 14

Fair warning: the DynamoDB connector depends on DQL which recently became unmaintained. I’ve found lots of issues with the DQL connector and would not recommend Redash for Dynamo users unless you use an intermediary like Rockset or Stitch. For simple use-cases it’s still serviceable. But for power users without a better ETL solution it’s not the right fit.