Documentation Index
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A scalar function.
Extracts a cardinality estimate of a
single Apache DataSketches HLL sketches that was previously built
using the aggregate
function APACHE_DATASKETCHES_HLL_BUILD.
The APACHE_DATASKETCHES_HLL_ESTIMATE function is used to estimate the cardinality (number of unique elements) of a dataset represented by an HLL (HyperLogLog) sketch. This is particularly useful for large datasets where exact counting is computationally expensive.
Syntax
APACHE_DATASKETCHES_HLL_ESTIMATE
(<expression>)
Parameters
| Parameter | Description | Supported input types |
|---|
<expression> | An Apache DataSketches HLL sketches in a valid format, e.g. the output of the APACHE_DATASKETCHES_HLL_BUILD function. | BYTEA |
Return Type
BIGINT
Error Handling
If the input expression is not a valid Apache DataSketches HLL sketches, the function will raise an error.
Ensure that the input is correctly formatted and generated by the APACHE_DATASKETCHES_HLL_BUILD function.
Example
Following the example
in APACHE_DATASKETCHES_HLL_BUILD:
SELECT APACHE_DATASKETCHES_HLL_ESTIMATE(a) AS estimate
FROM sketch_of_data_to_count
ORDER BY 1;
| estimate (BIGINT) |
|---|
| 3333526 |
| 5001149 |
SELECT APACHE_DATASKETCHES_HLL_ESTIMATE(APACHE_DATASKETCHES_HLL_MERGE(a)) AS estimate
FROM sketch_of_data_to_count;
| hll_estimate (BIGINT) |
|---|
| 6673219 |
