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Discover how to effectively pass an ARRAY STRUCT to a JavaScript User-Defined Function (UDF) in BigQuery SQL with our comprehensive guide.
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How to Pass an ARRAY<STRUCT> to a JavaScript UDF in BigQuery SQL

When working with BigQuery, you might find yourself needing to pass complex data structures, such as ARRAY<STRUCT>, to a JavaScript UDF (User-Defined Function). This can be a bit tricky if you're unfamiliar with the syntax and the proper way to structure your data. In this guide, we'll walk you through the problem, provide the solution, and explain key concepts along the way to ensure your queries work seamlessly.

The Problem

You're trying to obtain data from multiple tables and utilize these in a JavaScript UDF within BigQuery. You have successfully declared your arrays and UDF but encountered some syntax issues when attempting to pass arg2 as an ARRAY<STRUCT>.

The initial code you wrote looked promising, yet there were a few errors that need to be fixed to achieve your goal.

The Proposed Solution

Overview of Fixes

We will make several improvements to the original query:

Retain arg1: Although you could include this data in the TBL1 CTE, keeping arg1 separate for clarity is beneficial.

Define arg2 Correctly: We need to create arg2 by selecting from TBL1 as STRUCT with the proper column names.

Ensure Data Types Match: Since myfunction accepts col2 as a string, we must cast SchoolID as a string.

Include Additional Fields: Adding an id field will help in grouping or aggregating data.

Format the Final Selection: Properly pass the arguments to your UDF and use array_agg to structure your data correctly.

The Corrected SQL Query

Here’s the improved version of your SQL code:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Key Changes

ARRAY Declaration: The declaration of arg1 remains unchanged, but we restructured how arg2 is selected.

Using CTEs: The use of Common Table Expressions (CTEs) for TBL1 and tbl2 allows us to create structured data simply.

Type Casting: The SchoolID field is cast to a string with CAST(SchoolID as STRING), ensuring compatibility with the UDF.

Aggregation: The array_agg(arg2) function is used to gather all arg2 values into the proper structure needed by myfunction.

With these corrections, your query should now work effectively when passing an ARRAY<STRUCT> to a JavaScript UDF in BigQuery SQL!

Conclusion

Passing an ARRAY<STRUCT> into a JavaScript UDF in BigQuery can seem daunting at first, but with careful attention to syntax and structure, it's entirely achievable. By following the guidance outlined here, you'll be better equipped to work with complex data types and unleash the full power of BigQuery in your data processing tasks.

If you have any questions or run into further issues, feel free to ask for help!