APPROX_COUNT_DISTINCT

Description

Syntax

APPROX_COUNT_DISTINCT (expr)

Returns an approximate aggregation function similar to the result of COUNT (DISTINCT col).

It combines COUNT and DISTINCT faster and uses fixed-size memory, so less memory can be used for columns with high cardinality.

example

1. MySQL > select approx_count_distinct(query_id) from log_statis group by datetime;
2. +-----------------+
3. | approx_count_distinct(`query_id`) |
4. +-----------------+
5. | 17721           |
6. +-----------------+

keyword

APPROX_COUNT_DISTINCT