docs/source/user-guide/sql/information_schema.md

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# Information Schema

DataFusion supports showing metadata about the tables and views available. This information can be accessed using the
views of the ISO SQL `information_schema` schema or the DataFusion specific `SHOW TABLES` and `SHOW COLUMNS` commands.

## `SHOW TABLES`

To show tables in the DataFusion catalog, use the `SHOW TABLES` command or the
`information_schema.tables` view:

```sql
> show tables;
or
> select * from information_schema.tables;
+---------------+--------------------+------------+------------+
| table_catalog | table_schema       | table_name | table_type |
+---------------+--------------------+------------+------------+
| datafusion    | public             | t          | BASE TABLE |
| datafusion    | information_schema | tables     | VIEW       |
| datafusion    | information_schema | views      | VIEW       |
| datafusion    | information_schema | columns    | VIEW       |
+---------------+--------------------+------------+------------+

```

## `SHOW COLUMNS`

To show the schema of a table in DataFusion, use the `SHOW COLUMNS` command or
the `information_schema.columns` view.

```sql
> show columns from t;
or
> select table_catalog, table_schema, table_name, column_name, data_type, is_nullable from information_schema.columns;
+---------------+--------------+------------+-------------+-----------+-------------+
| table_catalog | table_schema | table_name | column_name | data_type | is_nullable |
+---------------+--------------+------------+-------------+-----------+-------------+
| datafusion    | public       | t          | Int64(1)    | Int64     | NO          |
+---------------+--------------+------------+-------------+-----------+-------------+
```

## `SHOW ALL` (configuration options)

To show the current session configuration options, use the `SHOW ALL` command or
the `information_schema.df_settings` view:

```sql
select * from information_schema.df_settings;

+-------------------------------------------------+---------+
| name                                            | setting |
+-------------------------------------------------+---------+
| datafusion.execution.batch_size                 | 8192    |
| datafusion.execution.coalesce_batches           | true    |
| datafusion.execution.time_zone                  | UTC     |
| datafusion.explain.logical_plan_only            | false   |
| datafusion.explain.physical_plan_only           | false   |
...
| datafusion.optimizer.filter_null_join_keys      | false   |
| datafusion.optimizer.skip_failed_rules          | true    |
+-------------------------------------------------+---------+
```

## `SHOW FUNCTIONS`

To show the list of functions available, use the `SHOW FUNCTIONS` command or the

- `information_schema.information_schema.routines` view: functions and descriptions
- `information_schema.information_schema.parameters` view: parameters and descriptions

Syntax:

```sql
SHOW FUNCTIONS [ LIKE <pattern> ];
```

Example output

```sql
> show functions like '%datetrunc';
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
| function_name | return_type                         | parameters              | parameter_types                                 | function_type | description                                           | syntax_example                    |
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
| datetrunc     | Timestamp(Microsecond, Some("+TZ")) | [precision, expression] | [Utf8, Timestamp(Microsecond, Some("+TZ"))]     | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, None)         | [precision, expression] | [Utf8View, Timestamp(Nanosecond, None)]         | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, Some("+TZ"))      | [precision, expression] | [Utf8View, Timestamp(Second, Some("+TZ"))]      | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, None)        | [precision, expression] | [Utf8View, Timestamp(Microsecond, None)]        | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, None)             | [precision, expression] | [Utf8View, Timestamp(Second, None)]             | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, None)        | [precision, expression] | [Utf8, Timestamp(Microsecond, None)]            | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, None)             | [precision, expression] | [Utf8, Timestamp(Second, None)]                 | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, Some("+TZ")) | [precision, expression] | [Utf8View, Timestamp(Microsecond, Some("+TZ"))] | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, Some("+TZ"))  | [precision, expression] | [Utf8, Timestamp(Nanosecond, Some("+TZ"))]      | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, None)        | [precision, expression] | [Utf8, Timestamp(Millisecond, None)]            | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, Some("+TZ")) | [precision, expression] | [Utf8, Timestamp(Millisecond, Some("+TZ"))]     | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, Some("+TZ"))      | [precision, expression] | [Utf8, Timestamp(Second, Some("+TZ"))]          | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, None)         | [precision, expression] | [Utf8, Timestamp(Nanosecond, None)]             | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, None)        | [precision, expression] | [Utf8View, Timestamp(Millisecond, None)]        | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, Some("+TZ")) | [precision, expression] | [Utf8View, Timestamp(Millisecond, Some("+TZ"))] | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, Some("+TZ"))  | [precision, expression] | [Utf8View, Timestamp(Nanosecond, Some("+TZ"))]  | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
16 row(s) fetched.
```