Write UDFs as external functions

You can write the executable code of a UDF in a language other than SQL.

• Register UDFs
  A UDF must be registered in the database before the function can be recognized and used by SQL.
• Pass arguments from DB2 to external functions
  DB2^® provides storage for all parameters passed to a UDF. Therefore, parameters are passed to the external function by address.
• Table function considerations
  An external table function is a UDF that delivers a table to the SQL in which it was referenced. A table function reference is only valid in a FROM clause of a SELECT statement.
• Error processing for UDFs
  When an error is encountered when processing a UDF, the system follows a specified model.
• Threads considerations
  A UDF, defined as FENCED, runs in the same job as the SQL statement that called it. However, the UDF runs in a system thread, separate from the thread that is running the SQL statement.
• Parallel processing
  A UDF can be defined to allow parallel processing.
• Fenced or unfenced considerations
  When creating a user-defined function (UDF) consider whether to make the UDF an unfenced UDF.
• Save and restore considerations
  When an external function associated with an ILE external program or service program is created, an attempt is made to save the function's attributes in the associated program or service program object.