trino how to filter json array

Guri Bee

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19-10-2024

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Introduction

In the world of data analytics and querying large datasets, Trino (formerly PrestoSQL) stands out as a powerful distributed SQL query engine. One of the popular use cases for Trino is querying JSON data, particularly when you're working with JSON arrays. In this article, we'll explore how to filter JSON arrays in Trino, providing practical examples and additional insights along the way.

Understanding JSON Data in Trino

Trino has built-in support for JSON data types. When you store JSON as a string, you can still access its contents using Trino's JSON functions. JSON arrays are commonly encountered in various applications, from APIs to configuration files, making it essential to master filtering them efficiently.

Example of a JSON Array

Consider the following JSON array representing a collection of books:

[
    {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925},
    {"title": "1984", "author": "George Orwell", "year": 1949},
    {"title": "To Kill a Mockingbird", "author": "Harper Lee", "year": 1960}
]

Filtering JSON Arrays in Trino

The Basic Query Structure

To query JSON arrays in Trino, you'll typically use the json_parse() function to convert a JSON string into a Trino JSON type. You can then leverage Trino's array functions to filter elements within the JSON array.

Filtering with JSON Functions

1. Using json_parse() and json_array_get(): This method allows you to filter specific elements from the JSON array by their index.

   SELECT json_array_get(json_parse('[{"title": "1984", "author": "George Orwell", "year": 1949}]'), 0) AS filtered_book;
   

   This query will return the first object from the JSON array.

2. Using json_extract() to Filter by Condition:

   You can also filter based on conditions using the json_extract() function to retrieve specific fields.

   SELECT
       json_extract(book, '$.title') AS title,
       json_extract(book, '$.author') AS author
   FROM
       (SELECT json_parse('[
           {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925},
           {"title": "1984", "author": "George Orwell", "year": 1949},
           {"title": "To Kill a Mockingbird", "author": "Harper Lee", "year": 1960}
       ]') AS books) AS t
   CROSS JOIN UNNEST(books) AS book
   WHERE json_extract(book, '$.year')::integer > 1940;
   

   In this query, we are filtering out books published after 1940 and selecting their titles and authors.

Advanced Filtering Techniques

Using ARRAY Functions

In addition to using JSON functions, you can utilize Trino's ARRAY functions for more complex filtering. For example, if you want to create an array of books published after 1940, you can use FILTER().

SELECT ARRAY_FILTER(books, book -> json_extract(book, '$.year')::integer > 1940) AS recent_books
FROM (SELECT json_parse('[
    {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925},
    {"title": "1984", "author": "George Orwell", "year": 1949},
    {"title": "To Kill a Mockingbird", "author": "Harper Lee", "year": 1960}
]') AS books) AS t;

This query would return a filtered array of books that meet the specified criteria.

Conclusion

Filtering JSON arrays in Trino can greatly enhance your data analytics capabilities. By leveraging Trino’s powerful JSON functions and array operations, you can extract meaningful insights from complex data structures.

Additional Tips for Working with JSON in Trino

• Indexing: When working with large JSON datasets, consider indexing your JSON data appropriately to speed up queries.
• Nested JSON: Be aware of nested JSON structures; you can access nested objects and arrays using dot notation or JSON path expressions.
• Performance: Regularly assess query performance and consider optimizing by breaking down complex queries into smaller, more manageable parts.

References

For more detailed queries and advanced usage, refer to the official Trino documentation. This article aims to provide practical insights and examples, but the official documentation is a comprehensive resource for deeper exploration.

Feel free to adapt these techniques to fit your unique data scenarios and enhance your JSON querying skills in Trino!

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