Documentazione di PostgreSQL 9.0 > Client Interfaces > The Information Schema > element_types
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34.19. element_types

The view element_types contains the data type descriptors of the elements of arrays. When a table column, domain, function parameter, or function return value is defined to be of an array type, the respective information schema view only contains ARRAY in the column data_type. To obtain information on the element type of the array, you can join the respective view with this view. For example, to show the columns of a table with data types and array element types, if applicable, you could do:

SELECT c.column_name, c.data_type, e.data_type AS element_type
FROM information_schema.columns c LEFT JOIN information_schema.element_types e
     ON ((c.table_catalog, c.table_schema, c.table_name, 'TABLE', c.dtd_identifier)
       = (e.object_catalog, e.object_schema, e.object_name, e.object_type, e.dtd_identifier))
WHERE c.table_schema = '...' AND c.table_name = '...'
ORDER BY c.ordinal_position;

This view only includes objects that the current user has access to, by way of being the owner or having some privilege.

Tabella 34.17. element_types Columns

NameData TypeDescription
object_catalogsql_identifier Name of the database that contains the object that uses the array being described (always the current database)
object_schemasql_identifier Name of the schema that contains the object that uses the array being described
object_namesql_identifier Name of the object that uses the array being described
object_typecharacter_data The type of the object that uses the array being described: one of TABLE (the array is used by a column of that table), DOMAIN (the array is used by that domain), ROUTINE (the array is used by a parameter or the return data type of that function).
dtd_identifiersql_identifier The identifier of the data type descriptor of the array being described
data_typecharacter_data Data type of the array elements, if it is a built-in type, else USER-DEFINED (in that case, the type is identified in udt_name and associated columns).
character_maximum_lengthcardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
character_octet_lengthcardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
character_set_catalogsql_identifierApplies to a feature not available in PostgreSQL
character_set_schemasql_identifierApplies to a feature not available in PostgreSQL
character_set_namesql_identifierApplies to a feature not available in PostgreSQL
collation_catalogsql_identifierApplies to a feature not available in PostgreSQL
collation_schemasql_identifierApplies to a feature not available in PostgreSQL
collation_namesql_identifierApplies to a feature not available in PostgreSQL
numeric_precisioncardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
numeric_precision_radixcardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
numeric_scalecardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
datetime_precisioncardinal_numberAlways null, since this information is not applied to array element data types in PostgreSQL
interval_typecharacter_dataAlways null, since this information is not applied to array element data types in PostgreSQL
interval_precisioncharacter_dataAlways null, since this information is not applied to array element data types in PostgreSQL
domain_defaultcharacter_dataNot yet implemented
udt_catalogsql_identifier Name of the database that the data type of the elements is defined in (always the current database)
udt_schemasql_identifier Name of the schema that the data type of the elements is defined in
udt_namesql_identifier Name of the data type of the elements
scope_catalogsql_identifierApplies to a feature not available in PostgreSQL
scope_schemasql_identifierApplies to a feature not available in PostgreSQL
scope_namesql_identifierApplies to a feature not available in PostgreSQL
maximum_cardinalitycardinal_numberAlways null, because arrays always have unlimited maximum cardinality in PostgreSQL

Documentazione di PostgreSQL 9.0 > Client Interfaces > The Information Schema > element_types
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