ClickHouse/docs/en/query_language/functions/ext_dict_functions.md

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# Functions for Working with External Dictionaries {#ext_dict_functions}
For information on connecting and configuring external dictionaries, see [External dictionaries](../dicts/external_dicts.md).
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## dictGet {#dictget}
Retrieves a value from an external dictionary.
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``` sql
dictGet('dict_name', 'attr_name', id_expr)
dictGetOrDefault('dict_name', 'attr_name', id_expr, default_value_expr)
```
**Parameters**
- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `attr_name` — Name of the column of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md) or [Tuple](../../data_types/tuple.md)-type value depending on the dictionary configuration.
- `default_value_expr` — Value returned if the dictionary doesnt 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.
**Returned value**
- If ClickHouse parses the attribute successfully in the [attributes data type](../../query_language/dicts/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:
- `dictGet` returns the content of the `<null_value>` element specified for the attribute in the dictionary configuration.
- `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 doesnt 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
1,1
2,2
```
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The first column is `id`, the second column is `c1`.
Configure the external dictionary:
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``` xml
<yandex>
<dictionary>
<name>ext-dict-test</name>
<source>
<file>
<path>/path-to/ext-dict-test.csv</path>
<format>CSV</format>
</file>
</source>
<layout>
<flat />
</layout>
<structure>
<id>
<name>id</name>
</id>
<attribute>
<name>c1</name>
<type>UInt32</type>
<null_value></null_value>
</attribute>
</structure>
<lifetime>0</lifetime>
</dictionary>
</yandex>
```
Perform the query:
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``` sql
SELECT
dictGetOrDefault('ext-dict-test', 'c1', number + 1, toUInt32(number * 10)) AS val,
toTypeName(val) AS type
FROM system.numbers
LIMIT 3
```
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``` text
┌─val─┬─type───┐
│ 1 │ UInt32 │
│ 2 │ UInt32 │
│ 20 │ UInt32 │
└─────┴────────┘
```
**See Also**
- [External Dictionaries](../dicts/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)
```
**Parameters**
- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md)-type value.
**Returned value**
- 0, if there is no key.
- 1, if there is a key.
Type: `UInt8`.
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## dictGetHierarchy {#dictgethierarchy}
Creates an array, containing all the parents of a key in the [hierarchical dictionary](../dicts/external_dicts_dict_hierarchical.md).
**Syntax**
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``` sql
dictGetHierarchy('dict_name', key)
```
**Parameters**
- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `key` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md)-type value.
**Returned value**
- Parents for the key.
Type: [Array(UInt64)](../../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
dictIsIn('dict_name', child_id_expr, ancestor_id_expr)
```
**Parameters**
- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `child_id_expr` — Key to be checked. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md)-type value.
- `ancestor_id_expr` — Alleged ancestor of the `child_id_expr` key. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md)-type value.
**Returned value**
- 0, if `child_id_expr` is not a child of `ancestor_id_expr`.
- 1, if `child_id_expr` is a child of `ancestor_id_expr` or if `child_id_expr` is an `ancestor_id_expr`.
Type: `UInt8`.
## 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.
Functions:
- `dictGetInt8`, `dictGetInt16`, `dictGetInt32`, `dictGetInt64`
- `dictGetUInt8`, `dictGetUInt16`, `dictGetUInt32`, `dictGetUInt64`
- `dictGetFloat32`, `dictGetFloat64`
- `dictGetDate`
- `dictGetDateTime`
- `dictGetUUID`
- `dictGetString`
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All these functions have the `OrDefault` modification. For example, `dictGetDateOrDefault`.
Syntax:
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``` sql
dictGet[Type]('dict_name', 'attr_name', id_expr)
dictGet[Type]OrDefault('dict_name', 'attr_name', id_expr, default_value_expr)
```
**Parameters**
- `dict_name` — Name of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `attr_name` — Name of the column of the dictionary. [String literal](../syntax.md#syntax-string-literal).
- `id_expr` — Key value. [Expression](../syntax.md#syntax-expressions) returning a [UInt64](../../data_types/int_uint.md)-type value.
- `default_value_expr` — Value which is returned if the dictionary doesnt 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.
**Returned value**
- If ClickHouse parses the attribute successfully in the [attributes data type](../../query_language/dicts/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:
- `dictGet[Type]` returns the content of the `<null_value>` element specified for the attribute in the dictionary configuration.
- `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 doesnt match the attribute data type.
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[Original article](https://clickhouse.tech/docs/en/query_language/functions/ext_dict_functions/) <!--hide-->