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 |
|---|---|---|
|
|
|
The expression for which to count distinct values |