In some old implementations of the BASIC programming language, user-defined functions are defined using the "DEF FN" syntax.
More modern dialects of BASIC are influenced by the structured programming paradigm, where most or all of the code is written as user-defined functions or procedures, and the concept becomes practically redundant.
In the COBOL programming language, a user-defined function is an entity that is defined by the user by specifying a FUNCTION-ID paragraph.
It invokes the CtoF user-defined function as declared above in order to convert the value in the column to a value in Fahrenheit.
The SQL standard defines the following properties: User-defined functions should not be confused with stored procedures.
Some database management systems allow the creation of user defined functions in languages other than SQL.
User-defined functions are subroutines made of one or more Transact-SQL statements that can be used to encapsulate code for reuse.
Does not allow changes to any Global Session State, like modifications to database or external resource, such as a file or network.
[2] Apache Doris, an open-source real-time analytical database, allows external users to contribute their own UDFs written in C++ to it.