Скачать или смотреть Resolving SQL compilation error: Unsupported subquery type cannot be evaluated in Snowflake UDTF

Learn how to troubleshoot and fix the `SQL compilation error: Unsupported subquery type cannot be evaluated` in Snowflake user-defined table functions with a practical example.
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This video is based on the question https://stackoverflow.com/q/62225083/ asked by the user 'Nathan T Alexander' ( https://stackoverflow.com/u/8377495/ ) and on the answer https://stackoverflow.com/a/62271461/ provided by the user 'Greg Pavlik' ( https://stackoverflow.com/u/12756381/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting the SQL Compilation Error: Unsupported Subquery Type Cannot Be Evaluated in Snowflake UDTF

When working with Snowflake, you might encounter various SQL errors, one of which is the frustrating Unsupported subquery type cannot be evaluated. This issue often arises when attempting to use user-defined table functions (UDTF) with subqueries that aren't supported. In this guide, we will explore the cause of this error and demonstrate a straightforward solution using JavaScript UDTFs.

Understanding the Problem

Let's dive into the scenario that triggers this error. You're trying to join a user-defined table function to a SELECT statement using values that aren't hardcoded, leading to the error mention. Specifically, the following SQL statement will produce the error:

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The error occurs because Snowflake doesn't support certain types of subqueries, and the method of calling the UDTF with dynamic input in this way is not valid.

The Context of Your Requirements

To clarify your needs, you mentioned that aside from solving this SQL error, your solution should accommodate numerous input arguments and output values. Using a single output scalar function would thus be inadequate. Therefore, an alternative approach is necessary.

The Solution: Switching to JavaScript UDTF

Although the native SQL UDTF implementation caused issues, we can resolve this by converting your function to a JavaScript UDTF. This method can effectively handle multiple inputs and return a table-like output without triggering the unsupported subquery error.

Step 1: Create the JavaScript UDTF

Here's how you can create the JavaScript version of your function:

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Step 2: Create Temporary Data Table

Make sure you have your temporary data table set up, as shown below:

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Step 3: Execute SQL Queries

Now, you can run your SQL queries without the unsupported subquery error. Below is an example that includes a similar dynamic execution without hardcoding values:

Hardcoded example (for testing)

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Dynamic values using LATERAL

To allow the UDTF to accept dynamic input, use the following SQL statement with LATERAL:

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Key Takeaways

When facing an unsupported subquery type error in Snowflake UDTFs, consider shifting to a JavaScript UDTF to handle complex data processing.

JavaScript UDTFs offer more flexibility and can efficiently manage multiple input arguments and provide table-like outputs.

Utilize LATERAL in your SQL queries to dynamically send inputs to your functions without hardcoding values.

By adopting a JavaScript UDTF approach, not only will you resolve the compilation error, but also enhance the performance and capability of your application handling more complex scenarios. Happy querying!