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).
## dictGet
Retrieves a value from an external dictionary.
```
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 [UInt64](../../data_types/int_uint.md)-typed value or [Tuple](../../data_types/tuple.md) depending on the dictionary configuration.
- `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 the value of the data type configured for the `attr_name` attribute.
**Returned value**
- If ClickHouse parses the attribute successfully with the [attribute's data type](../dicts/external_dicts_dict_structure.md#ext_dict_structure-attributes), functions return the value of the dictionary attribute that corresponds to `id_expr`.
- If there is no requested `id_expr` in the dictionary then:
- `dictGet` returns the content of the `<null_value>` element which is specified for the attribute in the dictionary configuration.
- `dictGetOrDefault` returns the value passed as the `default_value_expr` parameter.
ClickHouse throws an exception if it cannot parse the value of the attribute or the value doesn't match the attribute data type.
**Example of Use**
Create the text file `ext-dict-text.csv` with the following content:
```text
1,1
2,2
```
The first column is `id`, the second column is `c1`
Configure the external dictionary:
```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:
```sql
SELECT
dictGetOrDefault('ext-dict-test', 'c1', number + 1, toUInt32(number * 10)) AS val,
toTypeName(val) AS type
FROM system.numbers
LIMIT 3
```
```text
┌─val─┬─type───┐
│ 1 │ UInt32 │
│ 2 │ UInt32 │
│ 20 │ UInt32 │
└─────┴────────┘
```
**See Also**
- [External Dictionaries](../dicts/external_dicts.md)
## dictHas
Checks whether the dictionary has the key.
```
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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 [UInt64](../../data_types/int_uint.md)-typed value.
**Returned value**
- 0, if there is no key.
- 1, if there is a key.
Type: `UInt8`.
## dictGetHierarchy
For the hierarchical dictionary, returns an array of dictionary keys starting from passed `id_expr` and continuing along the chain of parent elements.
```
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dictGetHierarchy('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 [UInt64](../../data_types/int_uint.md)-typed value.
**Returned value**
Hierarchy of dictionary keys.
Type: Array(UInt64).
## dictIsIn
Checks the ancestor of a key in the hierarchical dictionary.
`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 that should be checked. [Expression](../syntax.md#syntax-expressions) returning [UInt64](../../data_types/int_uint.md)-typed value.
- `ancestor_id_expr` — Alleged ancestor of the `child_id_expr` key. [Expression](../syntax.md#syntax-expressions) returning [UInt64](../../data_types/int_uint.md)-typed 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}
ClickHouse supports the specialized functions that convert the dictionary attribute values to the strict data type independently of the configuration of the dictionary.
Functions:
- `dictGetInt8`, `dictGetInt16`, `dictGetInt32`, `dictGetInt64`
- `dictGetUInt8`, `dictGetUInt16`, `dictGetUInt32`, `dictGetUInt64`
- `dictGetFloat32`, `dictGetFloat64`
- `dictGetDate`
- `dictGetDateTime`
- `dictGetUUID`
- `dictGetString`
All these functions have the `OrDefault` modification. For example, `dictGetDateOrDefault`.
Syntax:
```
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 [UInt64](../../data_types/int_uint.md)-typed value.
- `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 the value of the data type configured for the `attr_name` attribute.
**Returned value**
- If ClickHouse parses the attribute successfully with the [attribute's data type](../dicts/external_dicts_dict_structure.md#ext_dict_structure-attributes), functions return the value of the dictionary attribute that corresponds to `id_expr`.
- If there is no requested `id_expr` in the dictionary then:
- `dictGet[Type]` returns the content of the `<null_value>` element which is specified for the attribute in the dictionary configuration.
- `dictGet[Type]OrDefault` returns the value passed as the `default_value_expr` parameter.
ClickHouse throws an exception, if it cannot parse the value of the attribute or the value doesn't match the attribute data type.
[Original article](https://clickhouse.yandex/docs/en/query_language/functions/ext_dict_functions/) <!--hide-->