APPROX_COUNT_DISTINCT

APPROX_COUNT_DISTINCT is a SQL function in the Aggregate Functions category. Approximate distinct count using HyperLogLog algorithm. Much faster than COUNT(DISTINCT) for large datasets. The syntax is APPROX_COUNT_DISTINCT(column). It accepts column. It returns approximate distinct count. A close relative is COUNT(), which returns the number of rows (or non-NULL values) in a group. A close relative is SUM(), which returns the sum of all non-NULL values in a group. Works with numeric columns. A close relative is AVG(), which returns the average (mean) of all non-NULL values in a group. More about this category: Aggregation functions — COUNT, SUM, AVG, MIN, MAX, GROUP BY, HAVING. Related Aggregate Functions entries: COUNT(), SUM(), AVG(), MIN(), MAX(), GROUP_CONCAT() / LISTAGG(), STRING_AGG(), VARIANCE() / VAR_SAMP(). This page is part of the free SQL Reference documentation covering 762+ statements, functions, and clauses, each with syntax, parameters, return values, and examples for MySQL, PostgreSQL, SQL Server, and SQLite.