element_typesThe 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 36.22. element_types Columns
| Name | Data 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. |