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An aggregate function. Returns an estimate of the number of distinct values for one or more HyperLogLog states.
APPROX_COUNT_DISTINCT_ESTIMATE ( expr )
An expression evaluating to a scalar value of type
VARBINARY(16384). This scalar value is the HyperLogLog state for which
APPROX_COUNT_DISTINCT_ESTIMATE returns the number of distinct values.
expr may be the name of a column. In this case,
APPROX_COUNT_DISTINCT_ESTIMATE combines values in the column (which are HyperLogLog states) and returns the number of distinct values in the combined state.
This function is used in conjuction with
APPROX_COUNT_DISTINCT_COMBINE. To best understand its usage, see the topic Distinct Count Estimation Functions.