presto array contains

Breiz Heurope

2 min read

·

06-03-2025

1

0

Share

Presto's ARRAY data type offers powerful ways to store and manipulate collections of values. But how do you efficiently check if an array contains a specific element? This guide dives deep into various methods for determining if a Presto array contains a particular value, covering different approaches and their performance implications. Understanding these techniques is crucial for writing efficient and effective Presto queries.

Understanding Presto Arrays

Before exploring the "contains" functionality, let's briefly review Presto arrays. Presto arrays are ordered lists of elements of the same data type. You can create them using the ARRAY constructor or through functions like array_concat. For instance:

SELECT ARRAY[1, 2, 3, 4, 5] AS my_array;

This creates an array named my_array containing the integers 1 through 5.

Methods to Check for Array Contains in Presto

Several methods exist to check if a Presto array contains a specific element. The optimal choice depends on your specific needs and data characteristics.

1. Using the CONTAINS Function (Most Efficient)

Presto offers a dedicated CONTAINS function specifically designed for checking array membership. This is generally the most efficient and straightforward approach:

SELECT CONTAINS(ARRAY[1, 2, 3, 4, 5], 3) AS contains_three; -- Returns TRUE
SELECT CONTAINS(ARRAY[1, 2, 3, 4, 5], 6) AS contains_six;  -- Returns FALSE

The CONTAINS function directly checks if the second argument (the element) exists within the array provided as the first argument. This function is optimized for this specific task and should be your preferred method.

2. Using the ARRAY_CONTAINS Function (Alternative Syntax)

Similar to CONTAINS, Presto also provides ARRAY_CONTAINS. This function offers a slightly different syntax but achieves the same result:

SELECT array_contains(ARRAY[1, 2, 3, 4, 5], 3) AS contains_three; -- Returns TRUE

Both CONTAINS and ARRAY_CONTAINS are functionally equivalent in most cases. Choose the one that best fits your coding style.

3. Manual Search with IN (Less Efficient, Avoid if Possible)

While possible, manually searching for an element using the IN operator within a CASE statement is generally less efficient than using the dedicated CONTAINS function. It's best to avoid this method unless absolutely necessary:

SELECT 
    CASE 
        WHEN 3 IN (SELECT * FROM UNNEST(ARRAY[1, 2, 3, 4, 5])) THEN TRUE
        ELSE FALSE 
    END AS contains_three; -- Returns TRUE

This method involves unnesting the array, which can significantly impact performance, especially with large arrays.

4. Using filter and size (For More Complex Scenarios)

For more complex scenarios, where you need to perform additional operations or filtering before checking for containment, combining the filter and size functions might be useful.

-- Example: Check if an array contains any even numbers
SELECT 
    CASE 
        WHEN size(filter(ARRAY[1, 2, 3, 4, 5], x -> x % 2 = 0)) > 0 THEN TRUE 
        ELSE FALSE 
    END AS contains_even; -- Returns TRUE

This approach filters the array to keep only even numbers and then checks if the resulting array has any elements. While functional, it's less direct and potentially less efficient than CONTAINS.

Performance Considerations

For optimal performance, always prioritize using the built-in CONTAINS function. It's specifically designed for this operation and will generally be the fastest approach. Avoid manual searching with IN and UNNEST whenever possible, as these methods are less efficient and can scale poorly with larger datasets.

Conclusion

Presto provides several ways to check if an array contains a specific element. While alternative methods exist, the CONTAINS function is the most efficient and recommended approach for its simplicity, readability, and optimized performance. Choosing the right method is key to writing efficient and scalable Presto queries that handle array data effectively. Remember to always prioritize the CONTAINS function for optimal performance in your Presto array operations.