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Showing content from https://clickhouse.com/docs/sql-reference/functions/ext-dict-functions below:

Functions for Working with Dictionaries

Note

For dictionaries created with DDL queries, the dict_name parameter must be fully specified, like <database>.<dict_name>. Otherwise, the current database is used.

For information on connecting and configuring dictionaries, see Dictionaries.

Retrieves values from a dictionary.

Arguments

• dict_name — Name of the dictionary. String literal.
• attr_names — Name of the column of the dictionary, String literal, or tuple of column names, Tuple(String literal.
• id_expr — Key value. Expression returning dictionary key-type value or Tuple-type value depending on the dictionary configuration.
• default_value_expr — Values returned if the dictionary does not contain a row with the id_expr key. Expression or Tuple(Expression), returning the value (or values) in the data types configured for the attr_names attribute.

Returned value

• If ClickHouse parses the attribute successfully in the attribute's data type, functions return the value of the dictionary attribute that corresponds to id_expr.

• 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.
  • dictGetOrNull returns NULL in case key was not found in dictionary.

ClickHouse throws an exception if it cannot parse the value of the attribute or the value does not match the attribute data type.

Example for simple key dictionary

Create a text file ext-dict-test.csv containing the following:

The first column is id, the second column is c1.

Configure the dictionary:

Perform the query:

Example for complex key dictionary

Create a text file ext-dict-mult.csv containing the following:

The first column is id, the second is c1, the third is c2.

Configure the dictionary:

Perform the query:

Example for range key dictionary

Input table:

Create the dictionary:

Perform the query:

Result:

See Also

• Dictionaries

Checks whether a key is present in a dictionary.

Arguments

• dict_name — Name of the dictionary. String literal.
• id_expr — Key value. Expression returning dictionary key-type value or Tuple-type value depending on the dictionary configuration.

Returned value

• 0, if there is no key. UInt8.
• 1, if there is a key. UInt8.

Creates an array, containing all the parents of a key in the hierarchical dictionary.

Syntax

Arguments

• dict_name — Name of the dictionary. String literal.
• key — Key value. Expression returning a UInt64-type value.

Returned value

• Parents for the key. Array(UInt64).

Checks the ancestor of a key through the whole hierarchical chain in the dictionary.

Arguments

• dict_name — Name of the dictionary. String literal.
• child_id_expr — Key to be checked. Expression returning a UInt64-type value.
• ancestor_id_expr — Alleged ancestor of the child_id_expr key. Expression returning a UInt64-type value.

Returned value

• 0, if child_id_expr is not a child of ancestor_id_expr. UInt8.
• 1, if child_id_expr is a child of ancestor_id_expr or if child_id_expr is an ancestor_id_expr. UInt8.

Returns first-level children as an array of indexes. It is the inverse transformation for dictGetHierarchy.

Syntax

Arguments

• dict_name — Name of the dictionary. String literal.
• key — Key value. Expression returning a UInt64-type value.

Returned values

• First-level descendants for the key. Array(UInt64).

Example

Consider the hierarchic dictionary:

First-level children:

Returns all descendants as if dictGetChildren function was applied level times recursively.

Syntax

Arguments

• dict_name — Name of the dictionary. String literal.
• key — Key value. Expression returning a UInt64-type value.
• level — Hierarchy level. If level = 0 returns all descendants to the end. UInt8.

Returned values

• Descendants for the key. Array(UInt64).

Example

Consider the hierarchic dictionary:

All descendants:

First-level descendants:

Retrieves the attribute values of all nodes that matched each key in a regular expression tree dictionary.

Besides returning values of type Array(T) instead of T, this function behaves similarly to dictGet.

Syntax

Arguments

• dict_name — Name of the dictionary. String literal.
• attr_names — Name of the column of the dictionary, String literal, or tuple of column names, Tuple(String literal).
• id_expr — Key value. Expression returning array of dictionary key-type value or Tuple-type value depending on the dictionary configuration.
• limit - Maximum length for each value array returned. When truncating, child nodes are given precedence over parent nodes, and otherwise the defined list order for the regexp tree dictionary is respected. If unspecified, array length is unlimited.

Returned value

• If ClickHouse parses the attribute successfully in the attribute's data type as defined in the dictionary, returns an array of dictionary attribute values that correspond to id_expr for each attribute specified by attr_names.

• If there is no key corresponding to id_expr in the dictionary, then an empty array is returned.

ClickHouse throws an exception if it cannot parse the value of the attribute or the value does not match the attribute data type.

Example

Consider the following regexp tree dictionary:

Get all matching values:

Get up to 2 matching values:

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
• dictGetIPv4, dictGetIPv6

All these functions have the OrDefault modification. For example, dictGetDateOrDefault.

Syntax:

Arguments

• dict_name — Name of the dictionary. String literal.
• attr_name — Name of the column of the dictionary. String literal.
• id_expr — Key value. Expression returning a UInt64 or Tuple-type value depending on the dictionary configuration.
• default_value_expr — Value returned if the dictionary does not contain a row with the id_expr key. Expression returning the value in the data type configured for the attr_name attribute.

Returned value

• If ClickHouse parses the attribute successfully in the attribute's data type, 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 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 does not match the attribute data type.

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