Hello, I've started exploring Pinot.. So is there any way to define primary key & foreign key relationships so that we can maintain mapping? Because, how will it support join without maintaining relationships?

Pinot only supports lookup join today https://docs.pinot.apache.org/users/user-guide-query/lookup-udf-join

So, there is no way to maintain relationships, right? We have use case like there is student table & subject table, which has foreign key relationship based on subjectID. So, is there any way by which it supports hibernate-ORM like functionality to update/modify child table(referenced) based on parent table(referencing) modification?

Not at the moment. You need to denormalize the tables upfront, or can use presto/trino for joins.

Okay, so is pinot not built for applications where we need relations or relational use case?

It is not a relational database, it is an OLAP datastore