approx_top_k | RawTree

Returns an array of the approximately most frequent values and their counts in the specified column.

Returns an array of the approximately most frequent values and their counts in the specified column. The resulting array is sorted in descending order of approximate frequency of values (not by the values themselves).

This function does not provide a guaranteed result. In certain situations, errors might occur and it might return frequent values that aren't the most frequent values.

Syntax

approx_top_k(N[, reserved])(column)

Parameters

N — The number of elements to return. Default value: 10. Maximum value of N = 65536. UInt64
reserved — Optional. Defines how many cells reserved for values. If uniq(column) > reserved, the result will be approximate. Default value: N * 3. UInt64

Arguments

column — The name of the column for which to find the most frequent values. String

Returned value

Returns an array of the approximately most frequent values and their counts, sorted in descending order of approximate frequency. Array

Examples

Usage example

SELECT approx_top_k(2)(k)
FROM VALUES('k Char, w UInt64', ('y', 1), ('y', 1), ('x', 5), ('y', 1), ('z', 10));

┌─approx_top_k(2)(k)────┐
│ [('y',3,0),('x',1,0)] │
└───────────────────────┘

Introduced in version 1.1.