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63 lines
1.5 KiB
Markdown
63 lines
1.5 KiB
Markdown
---
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toc_folder_title: Aggregate Functions
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toc_priority: 33
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toc_title: Introduction
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---
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# Aggregate Functions {#aggregate-functions}
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Aggregate functions work in the [normal](http://www.sql-tutorial.com/sql-aggregate-functions-sql-tutorial) way as expected by database experts.
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ClickHouse also supports:
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- [Parametric aggregate functions](../../sql-reference/aggregate-functions/parametric-functions.md#aggregate_functions_parametric), which accept other parameters in addition to columns.
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- [Combinators](../../sql-reference/aggregate-functions/combinators.md#aggregate_functions_combinators), which change the behavior of aggregate functions.
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## NULL Processing {#null-processing}
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During aggregation, all `NULL`s are skipped.
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**Examples:**
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Consider this table:
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``` text
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┌─x─┬────y─┐
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│ 1 │ 2 │
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│ 2 │ ᴺᵁᴸᴸ │
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│ 3 │ 2 │
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│ 3 │ 3 │
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│ 3 │ ᴺᵁᴸᴸ │
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└───┴──────┘
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```
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Let’s say you need to total the values in the `y` column:
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``` sql
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SELECT sum(y) FROM t_null_big
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```
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```text
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┌─sum(y)─┐
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│ 7 │
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└────────┘
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```
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Now you can use the `groupArray` function to create an array from the `y` column:
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``` sql
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SELECT groupArray(y) FROM t_null_big
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```
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``` text
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┌─groupArray(y)─┐
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│ [2,2,3] │
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└───────────────┘
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```
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`groupArray` does not include `NULL` in the resulting array.
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[Original article](https://clickhouse.tech/docs/en/query_language/agg_functions/) <!--hide-->
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