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hll_union

docs/en/sql-reference/sql-functions/aggregate-functions/hll_union.md

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hll_union

Returns the concatenation of a set of HLL values.

Syntax

Haskell
hll_union(hll)

Examples

Plain
mysql> select k1, hll_cardinality(hll_union(v1)) from tbl group by k1;
+------+----------------------------------+
| k1   | hll_cardinality(hll_union(`v1`)) |
+------+----------------------------------+
|    2 |                                4 |
|    1 |                                3 |
+------+----------------------------------+