kll_sketch_merge_double function

Applies to: Databricks Runtime 18.0 and later

Merges two compatible double KLL sketches into a single sketch.

Syntax

kll_sketch_merge_double ( sketch1, sketch2 )

Arguments

• sketch1: A BINARY expression containing a serialized DOUBLE KLL sketch.
• sketch2: A BINARY expression containing a serialized DOUBLE KLL sketch.

Returns

A BINARY value containing the merged sketch.

Notes

• Both sketches must be for the same data type (double).
• The merged sketch has the same k parameter as the input sketches.
• Sketches with different k values cannot be merged.
• Useful for distributed aggregation: create sketches per partition, then merge.

Examples

SQL

> WITH s1 AS (SELECT kll_sketch_agg_double(v) AS sketch FROM VALUES (1.0), (2.0) AS T(v)),
       s2 AS (SELECT kll_sketch_agg_double(v) AS sketch FROM VALUES (3.0), (4.0) AS T(v))
  SELECT kll_sketch_merge_double(s1.sketch, s2.sketch) FROM s1, s2
  [binary data]

Related functions

• kll_sketch_agg_double aggregate function
• kll_sketch_merge_bigint function
• kll_sketch_merge_float function