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hll_merge() (aggregation function)

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Merges HLL results across the group into a single HLL value.

  • Can be used only in context of aggregation inside summarize.

For more information, see the underlying algorithm (HyperLogLog) and estimation accuracy.

Syntax

hll_merge (Expr)

Arguments

  • Expr: Expression that will be used for the aggregation calculation.

Returns

The function returns the merged hll values of *Expr* across the group.

Tips

  1. Use the function dcount_hll to calculate the dcount from hll / hll-merge aggregation functions.