Скачать или смотреть How to Properly Use Arrays of Arrays in BigQuery

Discover how to effectively declare arrays of arrays in BigQuery, or explore alternative solutions like using array of structs.
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Understanding Arrays of Arrays in BigQuery

Working with arrays is a common requirement when managing data in BigQuery. However, you might run into limitations, especially when you try to declare arrays of arrays. This common scenario can lead to unexpected error messages when building your SQL procedures. In this guide, we’ll explore the problem of nested arrays and discuss an effective solution to this issue.

The Problem: Declaring Arrays of Arrays

When attempting to declare an array of arrays in BigQuery, you may encounter an error similar to this:

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This error signifies that BigQuery does not natively support directly nesting arrays within arrays. Below is an example that illustrates this error using a function and procedure.

Example Attempt

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In this script, the function attempts to return an array of arrays, which ultimately leads to a coercion error.

The Solution: Using Arrays of Structs

While arrays of arrays are not supported in BigQuery, you can achieve similar functionality by utilizing an array of structs. This approach allows you to encapsulate an array within a structured format. Here’s how you can do it:

1. Create an Array of Structs

Instead of an array of arrays, you can define your structure using structs in which each array element can be a struct containing an array. Here’s how to implement this:

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In this example:

Each struct contains an array, allowing you to organize data effectively.

The UNNEST function can be used to flatten the data for easy access during queries.

2. Modify Your Procedure

You can adapt your earlier procedure to accommodate this new structure. Here’s how the updated procedure would look:

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Key Takeaways

Nested arrays are not allowed in BigQuery; instead, use arrays of structs.

A struct allows you to group data systematically and provides better flexibility in accessing nested information.

Remember to use UNNEST to retrieve individual elements from your struct arrays when querying them.

By understanding and applying these concepts, you can efficiently handle complex data structures within BigQuery, avoiding common pitfalls associated with array nesting. If you encounter any challenges or have questions, feel free to reach out or leave a comment below!