What statement is allowed in a user-defined function?

In a user-defined function within SAP HANA, the use of JOIN statements is permitted as these functions are typically designed to return a single value or table based on the input parameters. Utilizing JOINs allows the function to access and combine data from multiple tables, which is crucial for creating complex data relationships and aggregating information as needed.

By integrating JOINs, user-defined functions can provide more sophisticated logic and insights derived from various data sources within the database, making them highly versatile for users who need to manipulate and analyze data. In contrast, statements like INSERT, COMMIT, and EXEC are not allowed in user-defined functions as they alter data or execute commands that are not suitable within the scope of function execution, which is designed to be transactional and non-destructive to the database state.

This understanding emphasizes the importance of JOINs for effective data handling in user-defined functions in SAP HANA, showcasing their capability to perform complex queries while maintaining the integrity and structure of the data environment.