approx_count_distinct
Description
Returns the approximate value of aggregate function similar to the result of COUNT(DISTINCT col).
It is faster than the COUNT and DISTINCT combination and uses a fixed-size memory, so less memory is used for columns of high cardinality.
Syntax
APPROX_COUNT_DISTINCT(expr)
Examples
MySQL > select approx_count_distinct(query_id) from log_statis group by datetime;
+-----------------------------------+
| approx_count_distinct(`query_id`) |
+-----------------------------------+
| 17721 |
+-----------------------------------+
keyword
APPROX_COUNT_DISTINCT