JIRA API support for Group by and GraphQL

Question

Problem:

We are looking to fetch number of issues closed over a certain duration and categorized by user and issue type (and may be more attributes in future).

Questions:

1. Does Jira JQL API support "Group By" clause?
2. If no, is there any other way to do this?
3. Slightly unrelated question - Does Jira API support GraphQL?

Answer 1

As far as I know, these are the answers:

1. No.
2. The fastest would be to query DB directly via SQL or write your own REST API end-point via ScriptRunner's REST API capabilities (if this is on-premise Jira, not cloud).
3. No.