count_distinct
Counts all distinct non-null grouped values.
count_distinct(xs:list) -> intDescription
The count_distinct function returns the number of unique, non-null values in
xs.
xs: list
The values to count.
Examples
Count distinct values
from {x: 1}, {x: 2}, {x: 2}, {x: 3}
summarize unique=count_distinct(x)
{unique: 3}