Tuple DoubleSummary Sketch Functions

DoubleSummary sketches provide cardinality estimation with a single summary double value per key. Values are summed on key collisions. Supports percentile queries on the summary values.

Table of contents

1. Aggregation Functions
   1. ds_tuple_summary_sketch
   2. ds_tuple_summary_union
2. Scalar Functions
   1. ds_tuple_summary_estimate
   2. ds_tuple_summary_percentile
   3. ds_tuple_summary_stringify
3. DoubleSummary vs ArrayOfDoubles

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Aggregation Functions

ds_tuple_summary_sketch

Builds a DoubleSummary sketch. Duplicate keys have their values summed.

ds_tuple_summary_sketch(key, value) -> varbinary

Parameter	Type	Description
key	VARCHAR or BIGINT	Key to sketch
value	DOUBLE	Summary value (summed on collision)

ds_tuple_summary_union

Computes the union of multiple DoubleSummary sketches.

ds_tuple_summary_union(sketch) -> varbinary

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Scalar Functions

ds_tuple_summary_estimate

Returns the cardinality estimate (number of distinct keys).

ds_tuple_summary_estimate(sketch) -> double

ds_tuple_summary_percentile

Returns the percentile of summary values across all retained entries.

ds_tuple_summary_percentile(sketch, percentile) -> double

Parameter	Type	Description
sketch	VARBINARY	DoubleSummary sketch
percentile	DOUBLE	Percentile (0.0 to 100.0)

Example:

-- Median total spend per user
SELECT ds_tuple_summary_percentile(
    ds_tuple_summary_sketch(user_id, amount), 50.0
) AS median_spend
FROM orders;

ds_tuple_summary_stringify

ds_tuple_summary_stringify(sketch) -> varchar

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DoubleSummary vs ArrayOfDoubles

Property	DoubleSummary	ArrayOfDoubles
Value columns	1	1+
Percentile query	Yes	Via to_quantiles_sketch
T-test	No	Yes
Means/Variances	No	Yes
Simplicity	Simpler	More powerful

Use DoubleSummary for simple “one value per key” scenarios where you want direct percentile access. Use ArrayOfDoubles when you need statistical comparisons or multiple value columns.