Solving the ARRAY_AGG Dilemma in User-Defined Functions on BigQuery

Описание: Discover an easy solution for using `ARRAY_AGG` within user-defined functions in BigQuery while extracting email addresses from messy datasets.
---
This video is based on the question https://stackoverflow.com/q/62988219/ asked by the user 'neydroydrec' ( https://stackoverflow.com/u/717441/ ) and on the answer https://stackoverflow.com/a/62988345/ provided by the user 'Mikhail Berlyant' ( https://stackoverflow.com/u/5221944/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: ARRAY_AGG not allowed in user-defined function (Standard SQL)

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Solving the ARRAY_AGG Dilemma in User-Defined Functions on BigQuery

Working with data in Google BigQuery can often come with its own set of challenges. A common issue faced by many developers is trying to leverage the powerful ARRAY_AGG() function inside user-defined functions (UDFs). This guide will address this challenge head-on and provide clear solutions.

The Challenge: ARRAY_AGG Not Allowed in UDFs

Recently, a user encountered a significant obstacle while creating a UDF to extract email addresses from a tumultuous dataset. The specific error revolved around the inability to use the ARRAY_AGG() function within the UDF. Here's a brief overview of the scenario:

The user attempted to construct a temporary function, GET_EMAIL, intended to take in an array of email addresses and an index to retrieve a distinct email based on the provided index.

The initial implementation utilized ARRAY_AGG() but was met with limitations since it isn't permitted within UDFs.

Initial Attempt

The original function attempted to aggregate distinct email entries and return the email at the specified index. Here's a snippet of that attempt:

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

Solution: Working Alternatives

After some trial and error, a couple of alternative methods surfaced that allow successfully retrieving email addresses without hitting the roadblocks presented by ARRAY_AGG().

Alternative Method 1: Simplified SELECT Array

The first corrective measure involves using a SELECT ARRAY() construct. Here’s how you can implement it:

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

The above structure directly fetches an array of emails matching the pattern and returns the one located at the specified index. When a query is executed:

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

The result:

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

Alternative Method 2: Using ARRAY_AGG() Effectively

Interestingly, a minor adjustment to the previous form still maintains the inclusion of ARRAY_AGG() while adhering to constraints. Here’s the version that works:

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

Executing the same query yields the same successful result, and users can still take advantage of the distinct aggregation that was original intended.

Conclusion

In summary, when faced with restrictions like the one involving ARRAY_AGG inside BigQuery UDFs, there's no need to lose hope. By pivoting to other methods such as using a combination of SELECT ARRAY() or carefully constructed SELECT statements, you can effectively manipulate and extract the data you need.

Whether you're tackling your own data cleaning or just diving into the realm of SQL functions, the tips shared here will equip you with the tools necessary to overcome similar challenges.

Final Thoughts

Now that you have an understanding of how to handle the limitations of ARRAY_AGG() in UDFs, keep these methods handy for your next BigQuery project. Happy querying!