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# Beam SQL overview

Beam SQL allows a Beam user (currently only available in Beam Java) to query
bounded and unbounded `PCollections` with SQL statements. Your SQL query
is translated to a `PTransform`, an encapsulated segment of a Beam pipeline.
You can freely mix SQL `PTransforms` and other `PTransforms` in your pipeline.

Beam SQL includes the following dialects:

- [Beam Calcite SQL](http://calcite.apache.org)
- [Beam ZetaSQL](https://github.com/google/zetasql)

Beam Calcite SQL is a variant of Apache Calcite, a dialect widespread in
big data processing. Beam Calcite SQL is the default Beam SQL dialect. Beam ZetaSQL is more compatible with BigQuery, so it's especially useful in pipelines that [write to or read from BigQuery tables](https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.html).

To change dialects, pass [the dialect's full package name](https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/extensions/sql/package-summary.html) to the [`setPlannerName`](https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/extensions/sql/impl/BeamSqlPipelineOptions.html#setPlannerName-java.lang.String-) method in the [`PipelineOptions`](https://beam.apache.org/releases/javadoc/2.15.0/org/apache/beam/sdk/options/PipelineOptions.html) interface.

There are two additional concepts you need to know to use SQL in your pipeline:

 - [SqlTransform](https://beam.apache.org/releases/javadoc/{{ site.release_latest }}/index.html?org/apache/beam/sdk/extensions/sql/SqlTransform.html): the interface for creating `PTransforms` from SQL queries.
 - [Row](https://beam.apache.org/releases/javadoc/{{ site.release_latest }}/index.html?org/apache/beam/sdk/values/Row.html):
   the type of elements that Beam SQL operates on. A `PCollection<Row>` plays the role of a table.

## Walkthrough
The [SQL pipeline walkthrough]({{ site.baseurl
}}/documentation/dsls/sql/walkthrough) works through how to use Beam SQL with example code.

## Shell
The Beam SQL shell allows you to write pipelines as SQL queries without using the Java SDK. 
The [Shell page]({{ site.baseurl
}}/documentation/dsls/sql/shell) describes how to work with the interactive Beam SQL shell. 

## Apache Calcite dialect 
The [Beam Calcite SQL overview]({{ site.baseurl
}}/documentation/dsls/sql/calcite/overview) summarizes Apache Calcite operators,
functions, syntax, and data types supported by Beam Calcite SQL.

## ZetaSQL dialect
For more information on the ZetaSQL features in Beam SQL, see the [Beam ZetaSQL dialect reference]({{ site.baseurl
}}/documentation/dsls/sql/zetasql/overview).

To switch to Beam ZetaSQL, configure the [pipeline options](https://beam.apache.org/releases/javadoc/2.15.0/org/apache/beam/sdk/options/PipelineOptions.html) as follows:
```
setPlannerName("org.apache.beam.sdk.extensions.sql.zetasql.ZetaSQLQueryPlanner")
```

## Beam SQL extensions
Beam SQL has additional extensions leveraging Beam’s unified batch/streaming model and processing complex data types. You can use these extensions with all Beam SQL dialects.