Embedded SQL Programming Guide

Chapter 7. Writing User-Defined Functions (UDFs)

This chapter discusses the details of how you write your own UDF, the issues you need to consider, and the steps required to make your UDF operational. Specifically, the following major topics are discussed:

• "Interface between DB2 and a UDF"
• "Writing OLE Automation UDFs"
• "Scratchpad Considerations"
• "Table Function Considerations"
• "Scenarios for Using LOB Locators"
• "Other Coding Considerations"
• "Examples of UDF Code"
• "Debugging your UDF"

After a preliminary discussion on the interface between DB2 and a UDF, the remaining discussion concerns how you implement UDFs. The information on writing the UDF emphasizes the presence or absence of a scratchpad as one of the primary considerations.

Some general considerations in using this section are:

• A lot of important material on defining and using UDFs is presented in "User-Defined Functions (UDF)", and is not repeated here. This discussion concentrates on how you implement a UDF.

• In addition to successfully running the CREATE FUNCTION statement, you must perform the following steps in order to implement an external UDF:
  • Writing the UDF in either C, C++ or Java
  • Compiling the UDF
  • Linking the UDF
  • Testing and Debugging the UDF

  You can find information on compiling and linking UDFs in the DB2 SDK Building Applications book for your platform.

• You can invoke your UDF using OLE (Object Linking and Embedding) as described in this chapter.

Note that a sourced UDF, which is different from an external UDF, does not require an implementation in the form of a separate piece of code. Such a UDF uses the same implementation as its source function, along with many of its other attributes.

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