Mirror of <https://developer.salesforce.com/docs/data/data-cloud-query-guide/references/dc-sql-reference/approx-count-distinct.html> (Salesforce, Data 360 Query Guide), read 2026-10-23. Salesforce's own page is the authority; this copy exists because that site refuses non-browser readers.

`APPROX_COUNT_DISTINCT`

Applies to: ✅ Data 360 SQL ✅ Tableau Hyper API

Computes an approximation of the count of distinct values with a specified expected relative error.

<expression>: An expression of any type to count distinct values for.

<error>: A double precision value specifying the expected relative error. Must be in the range (0.002, 1]. Defaults to 0.023 (2.3% expected relative error).

Returns a bigint representing the approximate count of distinct values.

Faster than exact count(distinct expression) for large datasets.
The error parameter controls the trade-off between accuracy and performance.
Lower error values provide more accurate results but may require more computation.

Get an approximate count of distinct values.

Specify a custom error rate for higher accuracy.

Returns an approximate count with 1% expected relative error.