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Blargian 2024-04-09 12:34:53 +02:00
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docs/en/sql-reference/aggregate-functions/reference/uniqcombined.md
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@ -29,13 +29,13 @@ The `uniqCombined` function:
- Calculates a hash (64-bit hash for `String` and 32-bit otherwise) for all parameters in the aggregate, then uses it in calculations.
- Uses a combination of three algorithms: array, hash table, and HyperLogLog with an error correction table.
- For a small number of distinct elements, an array is used.
- When the set size is larger, a hash table is used.
- For a larger number of elements, HyperLogLog is used, which will occupy a fixed amount of memory.
- For a small number of distinct elements, an array is used.
- When the set size is larger, a hash table is used.
- For a larger number of elements, HyperLogLog is used, which will occupy a fixed amount of memory.
- Provides the result deterministically (it does not depend on the query processing order).
:::note
Since it uses 32-bit hash for non-`String` type, the result will have very high error for cardinalities significantly larger than `UINT_MAX` (error will raise quickly after a few tens of billions of distinct values), hence in this case you should use [uniqCombined64](../../../sql-reference/aggregate-functions/reference/uniqcombined64.md#agg_function-uniqcombined64)
Since it uses a 32-bit hash for non-`String` types, the result will have very high error for cardinalities significantly larger than `UINT_MAX` (error will raise quickly after a few tens of billions of distinct values), hence in this case you should use [uniqCombined64](../../../sql-reference/aggregate-functions/reference/uniqcombined64.md#agg_function-uniqcombined64).
:::
Compared to the [uniq](../../../sql-reference/aggregate-functions/reference/uniq.md#agg_function-uniq) function, the `uniqCombined` function: