Calculates the approximate number of different argument values, using the HyperLogLog algorithm.
The function takes a variable number of parameters. Parameters can be
String, or numeric types.
- A UInt64-type number.
Calculates a hash for all parameters in the aggregate, then uses it in calculations.
Uses the HyperLogLog algorithm to approximate the number of different argument values.
212 5-bit cells are used. The size of the state is slightly more than 2.5 KB. The result is not very accurate (up to ~10% error) for small data sets (<10K elements). However, the result is fairly accurate for high-cardinality data sets (10K-100M), with a maximum error of ~1.6%. Starting from 100M, the estimation error increases, and the function will return very inaccurate results for data sets with extremely high cardinality (1B+ elements).
Provides the determinate result (it doesn’t depend on the query processing order).