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38 lines
1.3 KiB
Markdown
38 lines
1.3 KiB
Markdown
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---
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toc_priority: 150
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---
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## initializeAggregation {#initializeaggregation}
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Initializes aggregation for your input rows. It is intended for the functions with the suffix `State`.
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Use it for tests or to process columns of types `AggregateFunction` and `AggregationgMergeTree`.
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**Syntax**
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``` sql
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initializeAggregation (aggregate_function, column_1, column_2);
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```
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**Parameters**
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- `aggregate_function` — Name of the aggregation function. The state of this function — the creating one. [String](../../../sql-reference/data-types/string.md#string).
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- `column_n` — The column to translate it into the function as it's argument. [String](../../../sql-reference/data-types/string.md#string).
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**Returned value(s)**
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Returns the result of the aggregation for your input rows. The return type will be the same as the return type of function, that `initializeAgregation` takes as first argument.
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For example for functions with the suffix `State` the return type will be `AggregateFunction`.
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**Example**
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Query:
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```sql
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SELECT uniqMerge(state) FROM (SELECT initializeAggregation('uniqState', number % 3) AS state FROM system.numbers LIMIT 10000);
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```
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Result:
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┌─uniqMerge(state)─┐
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│ 3 │
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└──────────────────┘
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