COUNT_DISTINCT

Description

Syntax

COUNT_DISTINCT(expr)

The number of rows used to return the required number, or the number of non-NULL rows

example

MySQL > select count_distinct(query_id) from log_statis group by datetime;
+----------------------------+
+ 124. Calculate (`query `uid') separately;
+----------------------------+
|                        577 |
+----------------------------+

keyword COUNT_DISTINCT,COUNT,DISTINCT