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Functions refer to user defined functions that are used to extend the processing capabilities of DeltaStream. There are already a number of built in functions available for users to use in their queries. Users can add more functions by implementing them and adding them to DeltaStream via Function declaration syntax.
There are three types of functions that users can declare in DeltaStream.
- UDFs or User Defined Functions: These functions can have zero or more arguments and return one value.
- UDAFs or User Defined Aggregate Functions: These functions compute values across multiple row (events) and return one value.
- UDTFs or User Defined Table Functions: There functions can have zero or more input arguments, however, they return multiple values that can result in multiple rows in the output.
DeltaStream is powered by Apache Flink so you can implement functions as Apache Flink user defined functions as described in Apache Flink documentation.
The implemented functions along with their dependencies should be packaged in a JAR file where it can be uploaded to DeltaStream. Once the JAR file is uploaded, a new function can be declared and added to the available functions. Then user can use the declared function in the experessions in their queries in DeltaStream.