kll_sketch_agg_double aggregate function

Applies to: Databricks Runtime 18.0 and later

Creates a KLL (K-Linear-Logarithmic) sketch for approximate quantile estimation on double precision floating-point data with configurable accuracy.

Syntax

kll_sketch_agg_double ( expr [, k] )

Arguments

• expr: A DOUBLE expression to aggregate.
• k: An optional INTEGER literal controlling sketch accuracy. Must be between 8 and 65535. The default is 200. Higher values provide better accuracy but use more memory.

Returns

A BINARY value containing the serialized KLL sketch for DOUBLE data.

Notes

• NULL values in expr are ignored during aggregation.
• NaN values are handled according to IEEE 754 semantics.
• The sketch provides approximate quantiles with a confidence level of about 99%.
• Preferred for high-precision quantile estimation.

Examples

SQL

-- Create sketch from double values
> SELECT kll_sketch_agg_double(measurement) FROM VALUES (1.23456), (2.34567) AS T(measurement)
  [binary data]

Related functions

• kll_sketch_agg_bigint aggregate function
• kll_sketch_agg_float aggregate function
• kll_sketch_get_quantile_bigint function
• kll_sketch_get_rank_bigint function