# Query metadata from a database
You can use the **Query metadata from a database** step to retrieve metadata from six different JDBC metadata discovery types. This is most useful with metadata injection.
| JDBC metadata discovery type | Description |
| ---------------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
| Catalog | Gets a list of catalogs from the database server. If the database does not support catalogs, this discovery type returns no rows. |
| Schemas | Gets a list of schemas from the database server. If the database does not support schemas, this discovery type returns no rows. |
| Tables | Gets a list of tables from the database. |
| Columns | Gets a list of columns from the database. |
| Primary keys | Gets a list of primary keys from the database. |
| Foreign keys | Gets a list of foreign keys from the database. |
{% hint style="info" %}
This step uses the standard JDBC API to collect metadata. Some database JDBC drivers do not fully implement the JDBC API. If you get unexpected results (including no data or partial results), try including a `%` in relevant pattern fields and/or upgrading your JDBC driver.
{% endhint %}
### General
* **Step name**: Specify the unique name of the **Query metadata from a database** step on the canvas. You can customize the name or leave it as the default.
### Connection tab
Use the **Connection** tab to connect to a JDBC database.
| Option | Description |
| ----------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Select connection** | Select a database connection from the list. You can also select **New** (create a connection), **Edit** (edit the selected connection), or **Wizard** (open the database connection wizard). |
| **From field** | Select a connection from fields available in the transformation data stream. |
| **Remove input fields** | If you use **From field**, select **Remove input fields** to omit the incoming connection fields from the output stream. |
### Input tab
Use the **Input** tab to filter results with values for each argument.
You can specify argument values in either of these ways:
* **Enter arguments**: Enter a value for an argument.
* **From fields**: Select an argument value from fields available in the transformation stream.
#### Enter arguments
Use this option to add values that filter the results.
* `%` matches 0 or more characters.
* `_` matches exactly 1 character.
| Discovery type | Argument | Description |
| -------------- | -------------- | --------------------------------------------------------------------------------------------------- |
| Schemas | Catalog | Name of the catalog to limit results. If empty, schemas from all catalogs are returned. |
| Schemas | Schema pattern | Pattern to limit schemas. If empty, schemas from all catalogs are returned. |
| Tables | Catalog | Name of the catalog to limit results. If empty, schemas from all catalogs are returned. |
| Tables | Schema pattern | Pattern to limit schemas. If empty, tables from all schemas are returned. |
| Tables | Table pattern | Pattern to limit tables. If empty, all tables are returned. |
| Tables | Table types | Comma-delimited list of table types to limit results. |
| Columns | Catalog | Name of the catalog to limit results. If empty, columns from all catalogs are returned. |
| Columns | Schema pattern | Pattern to limit schemas. If empty, columns from all schemas are returned. |
| Columns | Table pattern | Pattern to limit tables. This usually follows the database `LIKE` syntax (may vary by JDBC driver). |
| Columns | Column pattern | Pattern to limit columns. If empty, all columns are returned. |
| Primary keys | Catalog | Name of the catalog to limit results. If empty, schemas from all catalogs are returned. |
| Primary keys | Schema | Name of the schema to limit results. |
| Primary keys | Table | Name of the table to limit results. |
| Foreign keys | Catalog | Name of the catalog to limit results. If empty, schemas from all catalogs are returned. |
| Foreign keys | Schema | Name of the schema to limit results. |
| Foreign keys | Table | Name of the table to limit results. |
#### From fields
Use this option to filter results with values from the transformation stream. Select a value in one or more of the drop-down lists.
### Fields tab
Use the **Fields** tab to display the output fields for the selected discovery type.
1. Select the discovery type.
2. Select **Get fields**.
3. (Optional) Use **Rename to** to rename fields. Renamed fields are available to downstream steps.
Field names by discovery type
| JDBC metadata discovery type | Field name | Description |
| ---------------------------- | ------------------------------ | ------------------------------------------------------------------------------ |
| Catalog | `catalog` | Name of the database catalog |
| Schemas | `catalog` | Name of the database catalog |
| Schemas | `schema` | Name of the database schema |
| Tables | `catalog` | Name of the database catalog |
| Tables | `schema` | Name of the database schema |
| Tables | `ref_generation` | Reference generation |
| Tables | `remarks` | Remarks |
| Tables | `self_referencing_column_name` | A column that refers to another column in the same table |
| Tables | `table_name` | Name of the database table |
| Tables | `table_type` | Type of the database table |
| Tables | `type_catalog` | Type catalog |
| Tables | `type_name` | Type name |
| Tables | `type_schema` | Type schema |
| Columns | `buffer_length` | Length of the buffer for specific data types |
| Columns | `char_octet_length` | Maximum length (bytes) for binary data, character data, or text and image data |
| Columns | `column_default` | Default value of the column |
| Columns | `column_name` | Name of the column |
| Columns | `column_size` | Number of characters or digits of the data |
| Columns | `data_type` | Data type of the column |
| Columns | `decimal_digits` | Number of digits after the decimal point |
| Columns | `is_autoincrement` | Whether the column implements automatic increments |
| Columns | `is_generated_column` | Whether the column is generated |
| Columns | `is_nullable` | Whether the column allows null values |
| Columns | `nullable` | Column is nullable |
| Columns | `number_precision_radix` | Base system used for numeric precision (usually base 2 or 10) |
| Columns | `ordinal_position` | Location of the column ordering within a table or query output |
| Columns | `pentaho_data_type` | Custom Pentaho data type |
| Columns | `pentaho_data_type_int` | Custom Pentaho integer data type |
| Columns | `remarks` | Remarks |
| Columns | `schema` | Name of the database schema |
| Columns | `scope_catalog` | Catalog that lies within a scope |
| Columns | `scope_schema` | Schema that lies within a scope |
| Columns | `scope_table` | Table that lies within a scope |
| Columns | `source_data_type` | Data type within a source |
| Columns | `sql_data_type` | SQL data type for a column |
| Columns | `sql_datetime_sub` | SQL date/time sub |
| Columns | `table_name` | Name of a table in the database |
| Columns | `type_name` | Name of a type in a database |
| Primary keys | `catalog` | Name of the database catalog |
| Primary keys | `column_name` | Name of the column |
| Primary keys | `key_sequence` | Sequence of the primary key |
| Primary keys | `pk_name` | Name of the primary key |
| Primary keys | `schema` | Name of the database schema |
| Primary keys | `table_name` | Name of a table in the database |
| Foreign keys | `deferrability` | Whether the primary key has deferred constraints |
| Foreign keys | `delete_rule` | Delete rule for the primary key |
| Foreign keys | `fk_column_name` | Name of the foreign key column |
| Foreign keys | `fk_name` | Name of the foreign key |
| Foreign keys | `fk_table_schema` | Schema in the foreign key table |
| Foreign keys | `key_sequence` | Sequence of the foreign key |
| Foreign keys | `pk_column_name` | Name of the column in the primary key |
| Foreign keys | `pk_name` | Name of the primary key |
| Foreign keys | `pk_table_catalog` | Catalog that contains the primary key table |
| Foreign keys | `pk_table_name` | Name of the primary key table |
| Foreign keys | `pk_table_schema` | Schema in the primary key table |
| Foreign keys | `update_rule` | Update rule for the primary key |
### Metadata injection support
All fields of this step support metadata injection. You can use this step with [ETL metadata injection](/pdia-data-integration/pdi-transformation-steps-reference-overview/etl-metadata-injection.md) to pass metadata to your transformation at runtime.
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