MaxCompute provides SQL computing capabilities. In MaxCompute SQL, you can use the system’s built-in functions to perform certain computing and counting tasks. However, if such SQL functions do not meet your requirements, you can use the Java programming interface provided by MaxCompute to develop user-defined functions (for more information, see UDFs). UDFs can be divided into scalar valued functions, user-defined aggregate functions (UDAFs), and user-defined tables functions (UDTFs). UDFs are used in the same way as the built-in function, that is, you specify the UDF name, and input relevant parameters in SQL.
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.
For more information, see Function introduction.