countDistinct
Aggregate function.
The count(distinct ...) function calculates the uniq value of a set of values.
Note: NULL values are not counted.
Syntax​
COUNT(distinct arguments ...)
UNIQ(arguments)
Arguments​
| Arguments | Description |
|---|---|
| expression | Any expression, size of the arguments is [1, 32] |
Return Type​
UInt64
Examples​
mysql> SELECT count(distinct number % 3) FROM numbers(1000);
+------------------------------+
| count(distinct (number % 3)) |
+------------------------------+
| 3 |
+------------------------------+
mysql> SELECT uniq(number % 3, number) FROM numbers(1000);
+----------------------------+
| uniq((number % 3), number) |
+----------------------------+
| 1000 |
+----------------------------+
1 row in set (0.02 sec)
mysql> SELECT uniq(number % 3, number) = count(distinct number %3, number) FROM numbers(1000);
+---------------------------------------------------------------------+
| (uniq((number % 3), number) = count(distinct (number % 3), number)) |
+---------------------------------------------------------------------+
| true |
+---------------------------------------------------------------------+
1 row in set (0.03 sec