uniq

Calculates the approximate number of different values of the argument.

uniq(x[, ...])

Arguments

The function takes a variable number of parameters. Parameters can be Tuple, Array, Date, DateTime, String, or numeric types.

Returned value

A UInt64-type number.

Implementation details

Function:

Calculates a hash for all parameters in the aggregate, then uses it in calculations.
Uses an adaptive sampling algorithm. For the calculation state, the function uses a sample of element hash values up to 65536. This algorithm is very accurate and very efficient on the CPU. When the query contains several of these functions, using uniq is almost as fast as using other aggregate functions.
Provides the result deterministically (it does not depend on the query processing order).

We recommend using this function in almost all scenarios.

See Also

uniq

Introduced in: v1.1

Calculates the approximate number of different values of the argument.

The function uses an adaptive sampling algorithm. For the calculation state, the function uses a sample of element hash values up to 65536. This algorithm is very accurate and very efficient on the CPU. When the query contains several of these functions, using uniq is almost as fast as using other aggregate functions.

Implementation details

This function calculates a hash for all parameters in the aggregate, then uses it in calculations. It uses an adaptive sampling algorithm. For the calculation state, the function uses a sample of element hash values up to 65536. This algorithm is very accurate and very efficient on the CPU. When the query contains several of these functions, using uniq is almost as fast as using other aggregate functions.

Tip

We recommend using this function over other variants in almost all scenarios.

Syntax

uniq(x[, ...])

Arguments

x — The function takes a variable number of parameters. Tuple(T) or Array(T) or Date or DateTime or String or (U)Int* or Float* or Decimal

Returned value

Returns a UInt64-type number representing the approximate number of different values. UInt64

Examples

Example usage

CREATE TABLE example_table (
    id UInt32,
    category String,
    value Float64
) ENGINE = Memory;

INSERT INTO example_table VALUES
(1, 'A', 10.5),
(2, 'B', 20.3),
(3, 'A', 15.7),
(4, 'C', 8.9),
(5, 'B', 12.1),
(6, 'A', 18.4);

SELECT uniq(category) as unique_categories
FROM example_table;

┌─unique_categories─┐
│                 3 │
└───────────────────┘

Multiple arguments

SELECT uniq(category, value) as unique_combinations
FROM example_table;

┌─unique_combinations─┐
│                   6 │
└─────────────────────┘

uniq​

uniq