Relational Data - Aggregate Functions - Reference - Uniqthetasketch

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

• A UInt64-type number.

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

• uniq
• uniqCombined
• uniqCombined64
• uniqHLL12
• uniqExact