A coverage table, or a coverage factless table, is a type of a factless fact table when the primary fact table is spare and and you need to generate the negative report. For example, you can create a sales promotion factless table to store all the sales promotion for every week. Although you have provided various sales promotions, the actual sales may not happen for all promotions on each day. Creating a coverage table to store the possible combinations is far more efficient then store the sales promotions which is going on for a given day but it did not generate any sale as a fact record in the primary fact itself. The volume of the records in the sales fact table is much reduced if we create a separate coverage table.