Database schema of comments I would like to clarify the database table relationship between comment &amp; field_data_comment_body.

Questions are:


Is comment's body saved in field_data_comment_body table?
Is comment's cid = comment_body's entity_id ?
Is there any table other than these 2 contributed to comments?
Yes.
Combined with 'entity_type' = 'comment', yes. An entity (comment, node, term, user, ..) is always identified by their entity_type and entity_id.
Not directly, in this case. There is also field_revision_comment_body table, which is in this case not used because comments don't support revisions (but field always needs to create one because nothing stops you from adding that field to a node and create revisions of it). There are also the field_config and field_instance_config tables which contain information about which field is attached to which entity type/bundle.