[Yandex Cloud documentation](../../index.md) > [Yandex DataLens](../index.md) > [Datasets](index.md) > Dataset settings

# Yandex DataLens dataset settings

A dataset works with sources in direct access mode: DataLens runs all data queries on the source side. Dataset settings determine how the dataset uses the source data.

## Connecting multiple tables {#multi-table}

If multiple tables are available in the data source, you can [merge](create-dataset.md#links) them using the JOIN operator.
When the tables are joined, a link is created between them. When you create a link, you specify the fields from the source table and merged table.

You can use the following types of JOIN operators:

* [INNER](https://en.wikipedia.org/wiki/Join_(SQL)#Inner_join)
* [LEFT](https://en.wikipedia.org/wiki/Join_(SQL)#Left_outer_join)
* [RIGHT](https://en.wikipedia.org/wiki/Join_(SQL)#Right_outer_join)
* [FULL](https://en.wikipedia.org/wiki/Join_(SQL)#Full_outer_join)

## Default filters for new charts {#default-filters}

In a dataset, you can [create](create-dataset.md#add-filters) a default filter. It will be applied to any new chart created from data in the current dataset.

{% note info %}

* You can create a filter for an individual chart in the chart settings.
* Default filters are not applied to data in the dataset preview area.

{% endnote %}

Default filters for new charts will enable you to:

* Reduce the amount of data requested from a source when building a chart.
* Add customized filters to new charts created from data in the same dataset.

## Running SQL queries in datasets {#sql-request-in-datatset}

You can define a dataset data source using ad-hoc SQL queries over database connections. When a data source is accessed, the query code runs as a subquery. For more information on how to use SQL queries in a dataset, see [Adding data](create-dataset.md#add-data).
When using SQL queries in datasets, we recommend:

* Limiting to `read-only` the permissions of the user stated in the connection.
* Granting the `Execute` access permission for the connection and associated datasets to users who should have no ad-hoc query privileges.

You can enable or disable the use of subqueries as a source when [creating](../concepts/connection/index.md) or editing a connection.


## Parameterization of dataset sources {#parametrization}

Parameterization of dataset sources allows you to dynamically substitute parameters from a chart into an SQL query or a table or schema name. For more information, see [Parameterization of dataset sources in Yandex DataLens](parametrization.md).


## Default preview {#preview-default}

By default, the dataset data uploaded from the source is displayed in the preview area. You can disable default data preview. To do this, click ![image](../../_assets/console-icons/gear.svg) → ![image](../../_assets/console-icons/check.svg) **Enable default preview** in the top-right corner of the dataset and save the dataset. Now, when you open the dataset, the data will not appear in the preview area. To display the data, click **Preview** at the top of the screen.

#### Useful links {#see-also}

* [Working with a dataset in Yandex DataLens](create-dataset.md)
* [Calculated fields in Yandex DataLens](../concepts/calculations/index.md)