Apache Drill allows users to explore any type of data using ANSI SQL. This is great, but Drill goes even further than that and allows you to create custom functions to extend the query engine. These custom functions have all the performance of any of the Drill primitive operations, but allowing that performance makes writing these functions a little trickier than you might expect.
In this article, I’ll explain step by step how to create and deploy a new function using a very basic example. Note that you can find lot of information about Drill Custom Functions in the documentation.
Let’s create a new function that allows you to mask some characters in a string, and let’s make it very simple. The new function will allow user to hide x number of characters from the start and replace then by any characters of their choice. This will look like:
You can find the full project in the following Github Repository.
As mentioned before, we could imagine many advanced features to this, but my goal is to focus on the steps to write a custom function, not so much on what the function does.