In case this is a database replication requirement, where you have yesterday's dump of a table from say another company's system and today's dump of that table from the same place and want to extract and apply the changes that took place in between, the full story of that using comm alone was (assuming table dumps come sorted, which can usually be arranged at dump time):

comm -23 table.yest table.today > table.deletes

comm -13 table.yest table.today > table.inserts

Each update is converted into one delete and one insert, so the deletes have to be processed first.