Extracts a cardinality estimate of a single HLL++ sketch that was previously built using the aggregate function HLL_COUNT_BUILD.

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Syntax

HLL_COUNT_ESTIMATE(<expression>)

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Parameters

ParameterDescriptionSupported input types
<expression>An HLL++ sketch produced by the HLL_COUNT_BUILD function.BYTEA

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Return Type

BIGINT

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Example

Following the example in HLL_COUNT_BUILD:

SELECT hll_count_estimate(a) AS hll_estimate
FROM sketch_of_data_to_count
ORDER BY 1;
hll_estimate (BIGINT)
3291008
4948957
SELECT hll_count_estimate(hll_count_merge(a)) AS hll_estimate
FROM sketch_of_data_to_count;
hll_estimate (BIGINT)
6606880