> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/client-interfaces/information-schema/infoschema-element-types.md).

# 35.24. 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 35.22. `element_types` Columns**

| <p>Column Type</p><p>Description</p>                                                                                                                                                                                                                                                                                                                                                                                                                          |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <p><code>object\_catalog</code> <code>sql\_identifier</code></p><p>Name of the database that contains the object that uses the array being described (always the current database)</p>                                                                                                                                                                                                                                                                        |
| <p><code>object\_schema</code> <code>sql\_identifier</code></p><p>Name of the schema that contains the object that uses the array being described</p>                                                                                                                                                                                                                                                                                                         |
| <p><code>object\_name</code> <code>sql\_identifier</code></p><p>Name of the object that uses the array being described</p>                                                                                                                                                                                                                                                                                                                                    |
| <p><code>object\_type</code> <code>character\_data</code></p><p>The type of the object that uses the array being described: one of <code>TABLE</code> (the array is used by a column of that table), <code>USER-DEFINED TYPE</code> (the array is used by an attribute of that composite type), <code>DOMAIN</code> (the array is used by that domain), <code>ROUTINE</code> (the array is used by a parameter or the return data type of that function).</p> |
| <p><code>collection\_type\_identifier</code> <code>sql\_identifier</code></p><p>The identifier of the data type descriptor of the array being described. Use this to join with the <code>dtd\_identifier</code> columns of other information schema views.</p>                                                                                                                                                                                                |
| <p><code>data\_type</code> <code>character\_data</code></p><p>Data type of the array elements, if it is a built-in type, else <code>USER-DEFINED</code> (in that case, the type is identified in <code>udt\_name</code> and associated columns).</p>                                                                                                                                                                                                          |
| <p><code>character\_maximum\_length</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                               |
| <p><code>character\_octet\_length</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                 |
| <p><code>character\_set\_catalog</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                               |
| <p><code>character\_set\_schema</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                                |
| <p><code>character\_set\_name</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                                  |
| <p><code>collation\_catalog</code> <code>sql\_identifier</code></p><p>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</p>                                                                                                                                                                                                                  |
| <p><code>collation\_schema</code> <code>sql\_identifier</code></p><p>Name of the schema containing the collation of the element type, null if default or the data type of the element is not collatable</p>                                                                                                                                                                                                                                                   |
| <p><code>collation\_name</code> <code>sql\_identifier</code></p><p>Name of the collation of the element type, null if default or the data type of the element is not collatable</p>                                                                                                                                                                                                                                                                           |
| <p><code>numeric\_precision</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                       |
| <p><code>numeric\_precision\_radix</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                |
| <p><code>numeric\_scale</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                           |
| <p><code>datetime\_precision</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                      |
| <p><code>interval\_type</code> <code>character\_data</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                            |
| <p><code>interval\_precision</code> <code>cardinal\_number</code></p><p>Always null, since this information is not applied to array element data types in PostgreSQL</p>                                                                                                                                                                                                                                                                                      |
| <p><code>udt\_catalog</code> <code>sql\_identifier</code></p><p>Name of the database that the data type of the elements is defined in (always the current database)</p>                                                                                                                                                                                                                                                                                       |
| <p><code>udt\_schema</code> <code>sql\_identifier</code></p><p>Name of the schema that the data type of the elements is defined in</p>                                                                                                                                                                                                                                                                                                                        |
| <p><code>udt\_name</code> <code>sql\_identifier</code></p><p>Name of the data type of the elements</p>                                                                                                                                                                                                                                                                                                                                                        |
| <p><code>scope\_catalog</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                                        |
| <p><code>scope\_schema</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                                         |
| <p><code>scope\_name</code> <code>sql\_identifier</code></p><p>Applies to a feature not available in PostgreSQL</p>                                                                                                                                                                                                                                                                                                                                           |
| <p><code>maximum\_cardinality</code> <code>cardinal\_number</code></p><p>Always null, because arrays always have unlimited maximum cardinality in PostgreSQL</p>                                                                                                                                                                                                                                                                                              |
| <p><code>dtd\_identifier</code> <code>sql\_identifier</code></p><p>An identifier of the data type descriptor of the element. This is currently not useful.</p>                                                                                                                                                                                                                                                                                                |

<br>

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/infoschema-element-types.html)（英文原文，待翻譯）


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