Writing Valid Custom SQL Metrics in Apache Superset Using Big Number Visualizations

Writing Valid Custom SQL Metrics in Apache Superset

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In this article, we will explore how to write a valid custom SQL metric in Apache Superset. We’ll delve into the world of Big Number visualizations and discuss potential errors that may occur while using such metrics.

Introduction to Custom SQL Metrics

Apache Superset is a popular data visualization platform that allows users to create interactive dashboards and reports. One of its features is support for custom SQL metrics, which enable users to calculate complex calculations on their data. In this article, we’ll focus on writing valid custom SQL metrics using the Big Number visualization type.

What are Big Number Visualizations?

Big Number visualizations allow you to display large numbers in a more readable format. They use a combination of JavaScript and CSS to render numbers with commas as thousand separators, decimal points, and currency symbols. This makes it easier to understand large numbers, such as monetary values or data sizes.

Writing Custom SQL Metrics

To write a custom SQL metric, you’ll need to follow these steps:

Define the Metric: In your Superset dashboard, navigate to the “Metrics” section and click on “New Metric”. Select the “Big Number” visualization type.
Enter the Formula: In the formula field, enter your custom SQL metric calculation. For example, if you want to calculate SUM(col_name)/2700000.0, your formula would look like this: SUM(col_name)/2700000.0
Save and Test: Click “Save” to save your metric, then navigate to the dashboard where you’re using the metric. You should see a new visualization with the calculated value.

Common Issues and Errors

While writing custom SQL metrics, you may encounter some common issues and errors:

ORA-00904: “col_name”: invalid identifier: This error occurs when the database engine cannot find the specified column (col_name) in your query. Make sure the column exists in your table.
SQL syntax errors: If your metric formula contains invalid SQL syntax, Superset will not render the visualization correctly.

Troubleshooting Tips

If you’re encountering issues with your custom SQL metric, try these troubleshooting tips:

Check your database schema: Verify that the column used in your metric formula exists and has the correct data type.
Use aliasing or quotes: If the column name contains special characters or is not recognized by Superset, use an alias (e.g., MY_SUM) or quotes (e.g., SUM("col_name")/2700000.0) to resolve the issue.

Fixing the ORA-00904 Error

The provided Stack Overflow post mentions a specific error (ORA-00904: "col_name": invalid identifier) that occurs when using custom SQL metrics in Apache Superset. This bug has been fixed in SQLAlchemy 1.3.5 and necessary changes have been made to the Superset master branch as of June 19, 2019.

Example Use Cases

Here are some example use cases for writing valid custom SQL metrics:

Calculating ratios: If you want to calculate a ratio between two columns, such as SUM(col1)/SUM(col2), your formula would look like this: SUM(col1)/SUM(col2)
Displaying percentages: To display a percentage value, use the following formula: (SUM(col_name)/MAX(SUM(col_name))) * 100

Conclusion

Writing valid custom SQL metrics in Apache Superset is an essential skill for data analysts and scientists. By understanding how to write these metrics using Big Number visualizations, you can create interactive dashboards that showcase your data insights. Remember to troubleshoot common issues, such as ORA-00904 errors, and use aliasing or quotes to resolve them.

Additional Resources

If you’re interested in learning more about custom SQL metrics in Apache Superset, here are some additional resources:

Last modified on 2024-06-07