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ClickHouse/docs/en/sql-reference/aggregate-functions/reference/uniqthetasketch.md
Pavel Kruglov 704bbe0aeb Raname uniqThetaSketch to uniqTheta
2021-05-11 17:39:35 +03:00

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uniqTheta

Calculates the approximate number of different argument values, using the Theta Sketch Framework.

uniqTheta(x[, ...])

Arguments

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

Returned value

Implementation details

Function:

  • Calculates a hash for all parameters in the aggregate, then uses it in calculations.

  • Uses the KMV algorithm to approximate the number of different argument values.

    4096(2^12) 64-bit sketch are used. The size of the state is about 41 KB.

  • The relative error is 3.125% (95% confidence), see the relative error table for detail.

See Also