olemus
funktsioon), mille loob
programmi või keskkonna kasutaja,
erinevalt sisseehitatuist

ülevaateid
https://www.techopedia.com/definition/3888/user-defined-function-udf

https://en.wikipedia.org/wiki/User-defined_function

näiteid
https://www.educba.com/c-plus-plus-user-defined-function/

https://simplesqltutorials.com/sql-server-user-defined-functions/

https://www.w3resource.com/python/python-user-defined-functions.php

https://docs.snowflake.com/en/developer-guide/udf/java/udf-java-introduction.html