Question

I see both COUNT and D_COUNT as options for aggregation. Which one should I use?

Answer

COUNT and D_COUNT, distinct counts, are ways of aggregating data. Data aggregation is the process of combining a list of items into one data point. For example, SUM is an aggregation where the listed values are added together.

COUNT counts the number of items being aggregated. D_COUNT counts the number of unique items there are being aggregated. Consider the list below.

Cat
Cat
Dog
Bird

If you aggregate the list above by COUNT, the list will show the result of 4 as there are four items. If you aggregate the same list by D_COUNT, the list will provide a result of 3 as two items are the same. The most common use for COUNT and D_COUNT in Explore is when aggregating ticket IDs. D_COUNT will ensure each ticket only shows up once, COUNT allows a ticket to be counted multiple times.

If a report has attributes in rows or columns, COUNT and D_COUNT are aggregated within each cell, not for the report as a whole. From the example above, imagine that "Cat," "Dog," and "Bird" are tags, and they are arranged on three tickets:

Ticket 1: Cat
Ticket 2: Cat, Dog
Ticket 3: Bird

COUNT and D_COUNT for tickets both return three since there are three tickets. However, if tags are added under rows, the total changes:

Cat: 2 tickets
Dog: 1 ticket
Bird: 1 ticket

The total is 4, even though there are only three tickets. This is because two unique tickets have the "Cat" tag. If a report has multiple rows or columns, the sum of D_COUNT values can be higher than the D_COUNT without rows or columns.

For more information on the different Explore aggregators, see the article: Choosing metric aggregators.