Aggregate Function Combinators
The name of an aggregate function can have a suffix appended to it. This changes the way the aggregate function works.
Distinct
Every unique combination of arguments will be aggregated only once. Repeating values are ignored.
count(distinct(expression))
sum(distinct(expression))
min(distinct(expression))
max(distinct(expression))
Examples
SELECT sum(distinct(number%3)) FROM numbers_mt(10);
+----------------------------+
| sum(distinct (number % 3)) |
+----------------------------+
| 3 |
+----------------------------+