Google BigQuery Delete Rows?

2 min read 08-10-2024

Understanding the Problem

Deleting rows from a dataset in Google BigQuery might not be as straightforward as it is in traditional databases. Due to the nature of how BigQuery is designed, especially since it is built for analytics on large datasets, performing row deletions requires some understanding of its structure. In this article, we will clarify how to effectively delete rows in BigQuery, provide an example of the process, and share best practices to optimize your workflow.

The Scenario

Imagine you have a dataset in BigQuery that stores customer information, and you need to delete certain rows where the customer's subscription has expired. The challenge here is how to carry out that deletion efficiently without disrupting other operations.

Original Code

Before we delve into how to delete rows, let’s take a look at the SQL command that you might think of using:

DELETE FROM `your_project.your_dataset.your_table`
WHERE subscription_status = 'expired';

However, while this syntax is correct, you need to understand a couple of caveats before executing this command.

Deleting Rows in BigQuery: Analysis and Clarifications

Understanding Delete Command: The DELETE statement in BigQuery is relatively straightforward; however, it only works on tables that support it (i.e., non-partitioned or partitioned tables). If you attempt to delete from a view or an external table, you will run into errors.
Handling Large Datasets: Deleting a large number of rows can be resource-intensive. Google BigQuery can handle deletes, but performance may degrade with larger datasets. In such cases, it might be more efficient to create a new table excluding the unwanted rows.
Querying for Validation: Always validate the data you want to delete by running a SELECT query first. This ensures you are targeting the right rows.
```
SELECT *
FROM `your_project.your_dataset.your_table`
WHERE subscription_status = 'expired';
```
Cost Considerations: Keep in mind that BigQuery charges for the amount of data processed. While deleting rows does not incur a cost, the subsequent querying and potential data copying might.

Best Practices for Deleting Rows

Use a Temporary Table: As mentioned, if you are looking at deleting a significant number of rows, consider creating a temporary table that includes only the data you want to keep. For instance:
```
CREATE OR REPLACE TABLE `your_project.your_dataset.new_table` AS
SELECT *
FROM `your_project.your_dataset.your_table`
WHERE subscription_status != 'expired';
```
After verifying the new table, you can rename it to replace the original table.
Schedule Regular Cleanups: For ongoing datasets, schedule regular clean-up tasks using Google Cloud Functions or Cloud Scheduler to maintain the dataset and delete expired subscriptions automatically.
Monitor Performance: Always monitor the performance of your BigQuery operations, especially after deletions, to ensure that queries continue to run efficiently.

Conclusion

Deleting rows in Google BigQuery can be accomplished using the DELETE statement, but understanding the underlying structure and implications of such actions is crucial. By following the best practices outlined in this article, you can maintain your datasets efficiently and optimize performance.

Additional Resources

By leveraging these insights, you can confidently manage your datasets in Google BigQuery and ensure your data is accurate and actionable.