Functions for Working with Embedded Dictionaries
In order for the functions below to work, the server config must specify the paths and addresses for getting all the embedded dictionaries. The dictionaries are loaded at the first call of any of these functions. If the reference lists can't be loaded, an exception is thrown.
As such, the examples shown in this section will throw an exception in ClickHouse Fiddle and in quick release and production deployments by default, unless first configured.
For information about creating reference lists, see the section "Dictionaries".
Multiple Geobases
ClickHouse supports working with multiple alternative geobases (regional hierarchies) simultaneously, in order to support various perspectives on which countries certain regions belong to.
The 'clickhouse-server' config specifies the file with the regional hierarchy:
<path_to_regions_hierarchy_file>/opt/geo/regions_hierarchy.txt</path_to_regions_hierarchy_file>
Besides this file, it also searches for files nearby that have the _ symbol and any suffix appended to the name (before the file extension).
For example, it will also find the file /opt/geo/regions_hierarchy_ua.txt, if present. Here ua is called the dictionary key. For a dictionary without a suffix, the key is an empty string.
All the dictionaries are re-loaded during runtime (once every certain number of seconds, as defined in the builtin_dictionaries_reload_interval config parameter, or once an hour by default). However, the list of available dictionaries is defined once, when the server starts.
All functions for working with regions have an optional argument at the end – the dictionary key. It is referred to as the geobase.
Example:
regionToName
Accepts a region ID and geobase and returns a string of the name of the region in the corresponding language. If the region with the specified ID does not exist, an empty string is returned.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Name of the region in the corresponding language specified by
geobase. String. - Otherwise, an empty string.
Example
Query:
Result:
regionToCity
Accepts a region ID from the geobase. If this region is a city or part of a city, it returns the region ID for the appropriate city. Otherwise, returns 0.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Region ID for the appropriate city, if it exists. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToArea
Converts a region to an area (type 5 in the geobase). In every other way, this function is the same as 'regionToCity'.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Region ID for the appropriate area, if it exists. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToDistrict
Converts a region to a federal district (type 4 in the geobase). In every other way, this function is the same as 'regionToCity'.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Region ID for the appropriate city, if it exists. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToCountry
Converts a region to a country (type 3 in the geobase). In every other way, this function is the same as 'regionToCity'.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Region ID for the appropriate country, if it exists. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToContinent
Converts a region to a continent (type 1 in the geobase). In every other way, this function is the same as 'regionToCity'.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Region ID for the appropriate continent, if it exists. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToTopContinent
Finds the highest continent in the hierarchy for the region.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Identifier of the top level continent (the latter when you climb the hierarchy of regions).UInt32.
- 0, if there is none.
Example
Query:
Result:
regionToPopulation
Gets the population for a region. The population can be recorded in files with the geobase. See the section "Dictionaries". If the population is not recorded for the region, it returns 0. In the geobase, the population might be recorded for child regions, but not for parent regions.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- Population for the region. UInt32.
- 0, if there is none.
Example
Query:
Result:
regionIn
Checks whether a lhs region belongs to a rhs region. Returns a UInt8 number equal to 1 if it belongs, or 0 if it does not belong.
Syntax
Parameters
lhs— Lhs region ID from the geobase. UInt32.rhs— Rhs region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
- 1, if it belongs. UInt8.
- 0, if it doesn't belong.
Implementation details
The relationship is reflexive – any region also belongs to itself.
Example
Query:
Result:
regionHierarchy
Accepts a UInt32 number – the region ID from the geobase. Returns an array of region IDs consisting of the passed region and all parents along the chain.
Syntax
Parameters
id— Region ID from the geobase. UInt32.geobase— Dictionary key. See Multiple Geobases. String. Optional.
Returned value
Example
Query:
Result: