1. A method comprising: receiving a request for a number of unique values within a set of values; calculating a first estimated count of unique values for the set of values; determining whether the first estimated count is within a particular count range; if it is determined that the first estimated count is within the particular count range, then: identifying, based on the first estimated count, a first value from a plurality of values that corresponds to the particular count range, and based on the first value and the first estimated count, calculating a second estimated count of unique values; and identifying the second estimated count as a response to the request; wherein the method is performed by one or more computing devices.