I really appreciate your efforts. Thanks!
Yes, I am using 2 bucketing aggregations, one for att1 and next for att2.
1> The rows in the data table are being split by using the "Terms" bucketing aggregation for both attributes.
2> The field name in the case of att1 is "projectname"
& in the case of att2 is "itemdisplayname"
3>No, "projectname" exists only in index A and "itemdisplayname" exists only in index C. {Now, is it possible?}