dynamodb query remove response duplicates in columns specified in ProjectionExpression

Question

Assume the following table, A is partition key, B is sort key:

A    B    C
a1   b1   c1
a1   b2   c1
a1   b3   c1
a1   b4   c2

If queried with KeyConditionExpression A=a1, ProjectionExpression C, return would be [c1, c1, c1, c2].

But I would like it to be [c1, c2], i.e. remove the duplicate c1.

How to do it?

Answer 1

As far as I know this is currently not possible.

Also, compared to removing duplicates by yourself after you received the result, would be a smaller result set is (and therefore maybe a little faster transmission). Even if it was possible the query would consume the same throughput capacity because DynamoDB internally would also need to query all results and then remove duplicates.