21.5. Aggregates Functions #
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approx_count_distinct(expression) returns#BIGINT Approximates the count of distinct elements using the HyperLogLog algorithm. This is much faster than
COUNT(DISTINCT ...)for large datasets, with a small error rate.Example 21.19.
-- Approximate distinct count of customer IDs SELECT approx_count_distinct(customer_id) FROM orders; -- Compare with exact count SELECT approx_count_distinct(customer_id) AS approx_distinct, COUNT(DISTINCT customer_id) AS exact_distinct FROM orders;Required parameters:
Name
Type
Description
expressionanyThe expression for which to count distinct values