39.24. `element_types`
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## 39.24. `element_types` #

The view `element_types` contains the data type descriptors of the elements of arrays. When a table column, composite-type attribute, 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.collection_type_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.

Table 39.22. `element_types` Columns

Column Type Description
`object_catalog` `sql_identifier` Name of the database that contains the object that uses the array being described (always the current database)
`object_schema` `sql_identifier` Name of the schema that contains the object that uses the array being described
`object_name` `sql_identifier` Name of the object that uses the array being described
`object_type` `character_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), `USER-DEFINED TYPE` (the array is used by an attribute of that composite type), `DOMAIN` (the array is used by that domain), `ROUTINE` (the array is used by a parameter or the return data type of that function).
`collection_type_identifier` `sql_identifier` The identifier of the data type descriptor of the array being described. Use this to join with the `dtd_identifier` columns of other information schema views.
`data_type` `character_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_length` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`character_octet_length` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`character_set_catalog` `sql_identifier` Applies to a feature not available in PostgreSQL
`character_set_schema` `sql_identifier` Applies to a feature not available in PostgreSQL
`character_set_name` `sql_identifier` Applies to a feature not available in PostgreSQL
`collation_catalog` `sql_identifier` Name of the database containing the collation of the element type (always the current database), null if default or the data type of the element is not collatable
`collation_schema` `sql_identifier` Name of the schema containing the collation of the element type, null if default or the data type of the element is not collatable
`collation_name` `sql_identifier` Name of the collation of the element type, null if default or the data type of the element is not collatable
`numeric_precision` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`numeric_precision_radix` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`numeric_scale` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`datetime_precision` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`interval_type` `character_data` Always null, since this information is not applied to array element data types in PostgreSQL
`interval_precision` `cardinal_number` Always null, since this information is not applied to array element data types in PostgreSQL
`domain_default` `character_data` Not yet implemented
`udt_catalog` `sql_identifier` Name of the database that the data type of the elements is defined in (always the current database)
`udt_schema` `sql_identifier` Name of the schema that the data type of the elements is defined in
`udt_name` `sql_identifier` Name of the data type of the elements
`scope_catalog` `sql_identifier` Applies to a feature not available in PostgreSQL
`scope_schema` `sql_identifier` Applies to a feature not available in PostgreSQL
`scope_name` `sql_identifier` Applies to a feature not available in PostgreSQL
`maximum_cardinality` `cardinal_number` Always null, because arrays always have unlimited maximum cardinality in PostgreSQL
`dtd_identifier` `sql_identifier` An identifier of the data type descriptor of the element. This is currently not useful.

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