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The Dataset Project ID is only required if the dataset is not in the same project that the BigQuery job will run in. The Dataset Project ID includes the Project ID where the dataset is stored and the name of the dataset (project-id:dataset-name). You can get dataset information in BigQuery. For more information, see Getting dataset information in the BigQuery documentation.
For example, you have a pipeline with a BigQuery Table batch source and want to run the BigQuery job in a project called project1. The dataset you want to read is stored in a project called inventory and the dataset is called us-inv, you would enter project1 in the Project ID field and inventory:us-inv in the Dataset Project ID field.
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