> ## Documentation Index
> Fetch the complete documentation index at: https://docs.prophecy.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Google BigQuery external table gem

> Read and write catalog tables in BigQuery

export const execution_engine_0 = "Prophecy Automate"

<Info>This gem runs in {execution_engine_0}.</Info>

## Overview

This page describes how to use BigQuery external Source and Target gems to read from or write to tables. Only use an external Source and Target gem when BigQuery is not the configured [SQL warehouse connection](/data-analysis/environment/fabrics/prophecy-fabrics). Otherwise, use the [Table gem](/data-analysis/gems/source-target/table/bigquery).

## Create a BigQuery gem

To create a BigQuery Source or Target gem in your pipeline:

<Steps>
  <Step title="Add a Source or Target gem to the pipeline">
    1. Open your pipeline in the [Studio](/data-analysis/development/studio/studio).
    2. Click on **Source/Target** in the canvas.
    3. Select **Source** or **Target** from the dropdown.
    4. Click on the gem to open the configuration.
  </Step>

  <Step title="Select BigQuery format">
    In the **Type** tab, select **BigQuery**. Then, click **Next**.
  </Step>

  <Step title="Set location details">
    In the **Location** tab, set your connection details and table location. To learn more, jump to [Source location](#source-location) and [Target location](#target-location).
  </Step>

  <Step title="Set table properties">
    In the **Properties** tab, set the table properties. To learn more, jump to [Source
    properties](#source-properties) and [Target properties](#target-properties).
  </Step>

  <Step title="Preview data (Source only)">
    In the **Preview** tab, load a sample of the data and verify that it looks correct.
  </Step>
</Steps>

## Source configuration

Use these settings to configure a BigQuery Source gem for reading data.

### Source location

| Parameter                   | Description                                                                                                                        |
| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| Format type                 | Table format for the source. For BigQuery tables, set to `bigquery`.                                                               |
| Select or create connection | Select or create a new [BigQuery connection](/data-analysis/environment/connections/bigquery) in the Prophecy fabric you will use. |
| Dataset                     | Dataset containing the table you want to read from.                                                                                |
| Name                        | Exact name of the BigQuery table to read data from.                                                                                |

### Source properties

Infer or manually configure the schema of your Source gem. Optionally, add a description for your table. Additional properties are not supported at this time.

## Target configuration

Use these settings to configure a BigQuery Target gem for writing data.

### Target location

| Parameter                   | Description                                                                                                                    |
| --------------------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| Format type                 | Table format for the target. For BigQuery tables, set to `bigquery`.                                                           |
| Select or create connection | Choose or create a [BigQuery connection](/data-analysis/environment/connections/bigquery) in the Prophecy fabric you will use. |
| Dataset                     | Dataset where the target table will be created or updated.                                                                     |
| Name                        | Name of the BigQuery table to write data to. If the table doesn't exist, it will be created automatically.                     |

### Target properties

| Property    | Description                                                                                                     | Default |
| ----------- | --------------------------------------------------------------------------------------------------------------- | ------- |
| Description | Description of the table.                                                                                       | None    |
| Write Mode  | Whether to overwrite the table completely, append new data to the table, or throw an error if the table exists. | None    |

## Cross-workspace access

If your fabric uses BigQuery as the SQL warehouse, you can't select BigQuery in an external Source or Target gem. Instead, you must use Table gems, which are limited to the BigQuery warehouse defined in the SQL warehouse connection.

To work with tables from a different BigQuery workspace, use [BigQuery sharing](https://cloud.google.com/bigquery/docs/analytics-hub-introduction). This lets you access shared resources without creating additional BigQuery connections.

<Info>
  Prophecy implements this guardrail to avoid using external connections when the data can be made
  available in your warehouse. External connections introduce an extra data transfer step, which
  slows down pipeline execution and adds unnecessary complexity. For best performance, Prophecy
  always prefers reading and writing directly within the warehouse.
</Info>