approx

Overview ¶

Package approx provides approximate aggregate functions.

Provided functions:

• approx_count_distinct(X, ...): approximate count of distinct elements using HyperLogLog.
• approx_count_distinct_accumulate(X, ...): accumulates elements into a HyperLogLog sketch BLOB.
• approx_count_distinct_combine(B): merges HyperLogLog sketch BLOBs into a single sketch BLOB.
• approx_count_distinct_estimate(B): estimates the cardinality from a HyperLogLog sketch BLOB.

Sketch BLOBs use the Aggregate Knowledge HLL Storage Specification (version 1), compatible with PostgreSQL's postgresql-hll extension.