This article gives you an overview of the functions that will be used in MaxCompute to provide you with computational functions.

MaxCompute provides SQL computing capabilities. In MaxCompute SQL, you can use the system’s built-in functions to perform common computing and counting tasks.  If the built-in functions do not meet your requirements, you can use the Java programming interface provided by MaxCompute to develop  user-defined functions (UDFs).

UDFs can be divided into scalar valued functions, user-defined aggregate functions (UDAFs), and user-defined tables functions (UDTFs). 

After writing the code for a UDF, you must compile the code into a JAR package and upload this package to MaxCompute. Then, you can register the UDF in MaxCompute.
Note UDFs are used in the same way as built-in functions, in that you specify the UDF name and input relevant parameters in SQL.

For more information,  see Function introduction.