Thanks @birthariyamayank !In this way, I understand that only primary identity will work in profile merge, so does identity graph have any practical effect? Especially in the segmentation service.Regards

There is a note in this document: A single schema may have many identity fields defined, but can only have one primary identity. All identity fields (primary or otherwise) contribute to the identity graph for an individual customer, but Real-Time Customer Profile uses only the primary identity as th...