mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-10-22 08:20:48 +00:00
193 lines
6.7 KiB
Markdown
193 lines
6.7 KiB
Markdown
# 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.
|
|
|
|
```
|
|
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.
|
|
|
|
```
|
|
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-->
|