Summarizing field types

[DavidKi]

Feature request:

Sometime users what, for example, count in one attribute of an entity the amount of sub entities or see summarized values of one field from all sub entities.
For this purpose it would be nice to have attribute field type for summarizing fields. There is already the SQL-Query field which could do this by theory. But in real world the user doesn't have access to the backend and even then it would be hard to code the wanted query.
So a front-end based "click-drag-drop-approach" would be needed: When creating the field in the data-model editor the user could select the field of the sub entity and the operand (count, sum...)

Or is this functionality already implemented?