APPROXIMATE_COUNT_DISTINCT

Purpose

This function returns the approximate number of distinct elements (without NULL).

Syntax

approximate_count_distinct::=

Approximate_Count_Distinct

Usage Notes

  • The result is not exact as it is with function COUNT, but it can be computed a lot faster.
  • For the calculation, the algorithm HyperLogLog is used internally.

Example

SELECT COUNT(DISTINCT customer_id) COUNT_EXACT,
APPROXIMATE_COUNT_DISTINCT (customer_id) COUNT_APPR
FROM orders WHERE price > 1000;
Result
COUNT_EXACT COUNT_APPR
10000000 10143194