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204 lines
7.3 KiB
Markdown
204 lines
7.3 KiB
Markdown
---
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toc_priority: 58
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toc_title: Working with External Dictionaries
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---
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# Functions for Working with External Dictionaries {#ext_dict_functions}
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For information on connecting and configuring external dictionaries, see [External dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
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## dictGet {#dictget}
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Retrieves a value from an external dictionary.
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``` sql
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dictGet('dict_name', 'attr_name', id_expr)
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dictGetOrDefault('dict_name', 'attr_name', id_expr, default_value_expr)
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```
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**Parameters**
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- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `attr_name` — Name of the column of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md) or [Tuple](../../sql-reference/data-types/tuple.md)-type value depending on the dictionary configuration.
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- `default_value_expr` — Value returned if the dictionary doesn’t contain a row with the `id_expr` key. [Expression](../syntax.md#syntax-expressions) returning the value in the data type configured for the `attr_name` attribute.
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**Returned value**
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- If ClickHouse parses the attribute successfully in the [attribute’s data type](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-attributes), functions return the value of the dictionary attribute that corresponds to `id_expr`.
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- If there is no the key, corresponding to `id_expr`, in the dictionary, then:
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- `dictGet` returns the content of the `<null_value>` element specified for the attribute in the dictionary configuration.
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- `dictGetOrDefault` returns the value passed as the `default_value_expr` parameter.
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ClickHouse throws an exception if it cannot parse the value of the attribute or the value doesn’t match the attribute data type.
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**Example**
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Create a text file `ext-dict-text.csv` containing the following:
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``` text
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1,1
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2,2
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```
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The first column is `id`, the second column is `c1`.
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Configure the external dictionary:
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``` xml
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<yandex>
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<dictionary>
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<name>ext-dict-test</name>
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<source>
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<file>
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<path>/path-to/ext-dict-test.csv</path>
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<format>CSV</format>
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</file>
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</source>
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<layout>
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<flat />
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</layout>
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<structure>
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<id>
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<name>id</name>
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</id>
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<attribute>
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<name>c1</name>
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<type>UInt32</type>
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<null_value></null_value>
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</attribute>
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</structure>
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<lifetime>0</lifetime>
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</dictionary>
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</yandex>
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```
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Perform the query:
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``` sql
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SELECT
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dictGetOrDefault('ext-dict-test', 'c1', number + 1, toUInt32(number * 10)) AS val,
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toTypeName(val) AS type
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FROM system.numbers
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LIMIT 3
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```
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``` text
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┌─val─┬─type───┐
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│ 1 │ UInt32 │
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│ 2 │ UInt32 │
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│ 20 │ UInt32 │
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└─────┴────────┘
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```
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**See Also**
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- [External Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md)
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## dictHas {#dicthas}
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Checks whether a key is present in a dictionary.
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``` sql
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dictHas('dict_name', id_expr)
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```
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**Parameters**
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- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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**Returned value**
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- 0, if there is no key.
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- 1, if there is a key.
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Type: `UInt8`.
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## dictGetHierarchy {#dictgethierarchy}
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Creates an array, containing all the parents of a key in the [hierarchical dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-hierarchical.md).
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**Syntax**
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``` sql
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dictGetHierarchy('dict_name', key)
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```
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**Parameters**
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- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `key` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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**Returned value**
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- Parents for the key.
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Type: [Array(UInt64)](../../sql-reference/data-types/array.md).
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## dictIsIn {#dictisin}
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Checks the ancestor of a key through the whole hierarchical chain in the dictionary.
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``` sql
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dictIsIn('dict_name', child_id_expr, ancestor_id_expr)
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```
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**Parameters**
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- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `child_id_expr` — Key to be checked. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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- `ancestor_id_expr` — Alleged ancestor of the `child_id_expr` key. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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**Returned value**
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- 0, if `child_id_expr` is not a child of `ancestor_id_expr`.
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- 1, if `child_id_expr` is a child of `ancestor_id_expr` or if `child_id_expr` is an `ancestor_id_expr`.
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Type: `UInt8`.
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## Other Functions {#ext_dict_functions-other}
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ClickHouse supports specialized functions that convert dictionary attribute values to a specific data type regardless of the dictionary configuration.
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Functions:
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- `dictGetInt8`, `dictGetInt16`, `dictGetInt32`, `dictGetInt64`
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- `dictGetUInt8`, `dictGetUInt16`, `dictGetUInt32`, `dictGetUInt64`
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- `dictGetFloat32`, `dictGetFloat64`
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- `dictGetDate`
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- `dictGetDateTime`
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- `dictGetUUID`
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- `dictGetString`
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All these functions have the `OrDefault` modification. For example, `dictGetDateOrDefault`.
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Syntax:
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``` sql
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dictGet[Type]('dict_name', 'attr_name', id_expr)
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dictGet[Type]OrDefault('dict_name', 'attr_name', id_expr, default_value_expr)
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```
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**Parameters**
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- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `attr_name` — Name of the column of the dictionary. [String literal](../syntax.md#syntax-string-literal).
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- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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- `default_value_expr` — Value which is returned if the dictionary doesn’t contain a row with the `id_expr` key. [Expression](../syntax.md#syntax-expressions) returning a value in the data type configured for the `attr_name` attribute.
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**Returned value**
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- If ClickHouse parses the attribute successfully in the [attribute’s data type](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-attributes), functions return the value of the dictionary attribute that corresponds to `id_expr`.
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- If there is no requested `id_expr` in the dictionary then:
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- `dictGet[Type]` returns the content of the `<null_value>` element specified for the attribute in the dictionary configuration.
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- `dictGet[Type]OrDefault` returns the value passed as the `default_value_expr` parameter.
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ClickHouse throws an exception if it cannot parse the value of the attribute or the value doesn’t match the attribute data type.
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[Original article](https://clickhouse.tech/docs/en/query_language/functions/ext_dict_functions/) <!--hide-->
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