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There is a mistake in section "Example for range key dictionary". The returned value is not correct.
444 lines
15 KiB
Markdown
444 lines
15 KiB
Markdown
---
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toc_priority: 58
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toc_title: External Dictionaries
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---
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!!! attention "Attention"
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For dictionaries, created with [DDL queries](../../sql-reference/statements/create/dictionary.md), the `dict_name` parameter must be fully specified, like `<database>.<dict_name>`. Otherwise, the current database is used.
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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, dictGetOrDefault, dictGetOrNull {#dictget}
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Retrieves values from an external dictionary.
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``` sql
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dictGet('dict_name', attr_names, id_expr)
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dictGetOrDefault('dict_name', attr_names, id_expr, default_value_expr)
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dictGetOrNull('dict_name', attr_name, id_expr)
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```
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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `attr_names` — Name of the column of the dictionary, [String literal](../../sql-reference/syntax.md#syntax-string-literal), or tuple of column names, [Tuple](../../sql-reference/data-types/tuple.md)([String literal](../../sql-reference/syntax.md#syntax-string-literal)).
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- `id_expr` — Key value. [Expression](../../sql-reference/syntax.md#syntax-expressions) returning dictionary key-type value or [Tuple](../../sql-reference/data-types/tuple.md)-type value depending on the dictionary configuration.
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- `default_value_expr` — Values returned if the dictionary does not contain a row with the `id_expr` key. [Expression](../../sql-reference/syntax.md#syntax-expressions) or [Tuple](../../sql-reference/data-types/tuple.md)([Expression](../../sql-reference/syntax.md#syntax-expressions)), returning the value (or values) in the data types configured for the `attr_names` 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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- `dictGetOrNull` returns `NULL` in case key was not found in dictionary.
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ClickHouse throws an exception if it cannot parse the value of the attribute or the value does not match the attribute data type.
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**Example for simple key dictionary**
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Create a text file `ext-dict-test.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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<clickhouse>
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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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</clickhouse>
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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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**Example for complex key dictionary**
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Create a text file `ext-dict-mult.csv` containing the following:
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``` text
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1,1,'1'
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2,2,'2'
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3,3,'3'
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```
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The first column is `id`, the second is `c1`, the third is `c2`.
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Configure the external dictionary:
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``` xml
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<clickhouse>
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<dictionary>
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<name>ext-dict-mult</name>
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<source>
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<file>
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<path>/path-to/ext-dict-mult.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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<attribute>
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<name>c2</name>
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<type>String</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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</clickhouse>
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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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dictGet('ext-dict-mult', ('c1','c2'), number) 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,'1') │ Tuple(UInt8, String) │
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│ (2,'2') │ Tuple(UInt8, String) │
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│ (3,'3') │ Tuple(UInt8, String) │
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└─────────┴───────────────────────┘
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```
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**Example for range key dictionary**
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Input table:
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```sql
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CREATE TABLE range_key_dictionary_source_table
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(
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key UInt64,
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start_date Date,
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end_date Date,
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value String,
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value_nullable Nullable(String)
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)
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ENGINE = TinyLog();
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INSERT INTO range_key_dictionary_source_table VALUES(1, toDate('2019-05-20'), toDate('2019-05-20'), 'First', 'First');
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INSERT INTO range_key_dictionary_source_table VALUES(2, toDate('2019-05-20'), toDate('2019-05-20'), 'Second', NULL);
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INSERT INTO range_key_dictionary_source_table VALUES(3, toDate('2019-05-20'), toDate('2019-05-20'), 'Third', 'Third');
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```
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Create the external dictionary:
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```sql
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CREATE DICTIONARY range_key_dictionary
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(
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key UInt64,
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start_date Date,
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end_date Date,
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value String,
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value_nullable Nullable(String)
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)
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PRIMARY KEY key
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SOURCE(CLICKHOUSE(HOST 'localhost' PORT tcpPort() TABLE 'range_key_dictionary_source_table'))
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LIFETIME(MIN 1 MAX 1000)
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LAYOUT(RANGE_HASHED())
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RANGE(MIN start_date MAX end_date);
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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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(number, toDate('2019-05-20')),
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dictHas('range_key_dictionary', number, toDate('2019-05-20')),
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dictGetOrNull('range_key_dictionary', 'value', number, toDate('2019-05-20')),
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dictGetOrNull('range_key_dictionary', 'value_nullable', number, toDate('2019-05-20')),
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dictGetOrNull('range_key_dictionary', ('value', 'value_nullable'), number, toDate('2019-05-20'))
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FROM system.numbers LIMIT 5 FORMAT TabSeparated;
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```
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Result:
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``` text
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(0,'2019-05-20') 0 \N \N (NULL,NULL)
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(1,'2019-05-20') 1 First First ('First','First')
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(2,'2019-05-20') 1 Second \N ('Second',NULL)
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(3,'2019-05-20') 1 Third Third ('Third','Third')
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(4,'2019-05-20') 0 \N \N (NULL,NULL)
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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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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `id_expr` — Key value. [Expression](../../sql-reference/syntax.md#syntax-expressions) returning dictionary key-type value or [Tuple](../../sql-reference/data-types/tuple.md)-type value depending on the dictionary configuration.
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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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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `key` — Key value. [Expression](../../sql-reference/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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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `child_id_expr` — Key to be checked. [Expression](../../sql-reference/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](../../sql-reference/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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## dictGetChildren {#dictgetchildren}
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Returns first-level children as an array of indexes. It is the inverse transformation for [dictGetHierarchy](#dictgethierarchy).
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**Syntax**
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``` sql
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dictGetChildren(dict_name, key)
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```
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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `key` — Key value. [Expression](../../sql-reference/syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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**Returned values**
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- First-level descendants for the key.
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Type: [Array](../../sql-reference/data-types/array.md)([UInt64](../../sql-reference/data-types/int-uint.md)).
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**Example**
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Consider the hierarchic dictionary:
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``` text
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┌─id─┬─parent_id─┐
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│ 1 │ 0 │
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│ 2 │ 1 │
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│ 3 │ 1 │
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│ 4 │ 2 │
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└────┴───────────┘
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```
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First-level children:
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``` sql
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SELECT dictGetChildren('hierarchy_flat_dictionary', number) FROM system.numbers LIMIT 4;
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```
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``` text
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┌─dictGetChildren('hierarchy_flat_dictionary', number)─┐
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│ [1] │
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│ [2,3] │
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│ [4] │
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│ [] │
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└──────────────────────────────────────────────────────┘
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```
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## dictGetDescendant {#dictgetdescendant}
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Returns all descendants as if [dictGetChildren](#dictgetchildren) function was applied `level` times recursively.
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**Syntax**
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``` sql
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dictGetDescendants(dict_name, key, level)
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```
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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `key` — Key value. [Expression](../../sql-reference/syntax.md#syntax-expressions) returning a [UInt64](../../sql-reference/data-types/int-uint.md)-type value.
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- `level` — Hierarchy level. If `level = 0` returns all descendants to the end. [UInt8](../../sql-reference/data-types/int-uint.md).
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**Returned values**
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- Descendants for the key.
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Type: [Array](../../sql-reference/data-types/array.md)([UInt64](../../sql-reference/data-types/int-uint.md)).
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**Example**
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Consider the hierarchic dictionary:
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``` text
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┌─id─┬─parent_id─┐
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│ 1 │ 0 │
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│ 2 │ 1 │
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│ 3 │ 1 │
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│ 4 │ 2 │
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└────┴───────────┘
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```
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All descendants:
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``` sql
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SELECT dictGetDescendants('hierarchy_flat_dictionary', number) FROM system.numbers LIMIT 4;
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```
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``` text
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┌─dictGetDescendants('hierarchy_flat_dictionary', number)─┐
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│ [1,2,3,4] │
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│ [2,3,4] │
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│ [4] │
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│ [] │
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└─────────────────────────────────────────────────────────┘
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```
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First-level descendants:
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``` sql
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SELECT dictGetDescendants('hierarchy_flat_dictionary', number, 1) FROM system.numbers LIMIT 4;
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```
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``` text
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┌─dictGetDescendants('hierarchy_flat_dictionary', number, 1)─┐
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│ [1] │
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│ [2,3] │
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│ [4] │
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│ [] │
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└────────────────────────────────────────────────────────────┘
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```
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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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**Arguments**
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- `dict_name` — Name of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `attr_name` — Name of the column of the dictionary. [String literal](../../sql-reference/syntax.md#syntax-string-literal).
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- `id_expr` — Key value. [Expression](../../sql-reference/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 does not contain a row with the `id_expr` key. [Expression](../../sql-reference/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 requested `id_expr` in the dictionary then:
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|
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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 does not match the attribute data type.
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