UDF Summary

MaxCompute provides many built-in functions to meet the computing requests of the users. A User Defined Function (UDF) is similar to any other Built-in Function. Users can create user-defined functions according to their computing requirements.

<dependency>
    <groupId>com.aliyun.odps</groupId>
    <artifactId>odps-sdk-udf</artifactId>
   <version>0.20.7-public</version>
</dependency>

In MaxCompute, you can expand two types of UDF:

UDF Class	Description
UDF(User Defined Scalar Function)	User Defined Scalar function. The relationship between input and output is a one-to-one relationship. Read a row data and write an output value.
UDTF (UserDefined Table Valued Function)	User-defined table valued functions are used in scenarios where the calling of one function leads to multiple rows of data being output. It is a unique user-defined function which can return multiple fields, while UDFcan only output a return value.
UDAF（User Defined Aggregation Function）	User Defined Aggregation Function (UDAF), the relationship between its input and output is one-to-many relationships. That is to aggregate multiple input records to an output value. It can be used with a Group By clause..  For more information, see Aggregation Functions.

Note

UDF stands for the set of user-defined functions, including User Defined Scalar Function, User Defined Aggregation Function and User Defined Table Valued Function. In a narrower sense, it represents user User Defined Scalar Function. The document uses this term frequently and the readers can judge the specific meaning according to the context . If the system prompts that memory is insufficient with an UDF involved in the SQL statement,  configure set  odps.sql.udf.joiner.jvm.memory=xxxx; to resolve this issue. This is because the data is huge and data skew also exists., This leads the memory size to occupythe task, which exceeds the default memory size.

MaxCompute UDF supports cross-project sharing. A UDF in project_b can be used in project_a.  For more information, , see Authorization in Security Guide documentation. other_project:udf_in_other_project(arg0, arg1) as res from table_t;。