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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​

ArgumentsDescription
expressionAny 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