| PostgreSQL 9.4.26 Documentation | |||
|---|---|---|---|
| Prev | Up | Chapter 34. The Information Schema | Next |
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 34-21. 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. |