type is specified as a parameter of the type. This parameter is called the 
target type of the reference. The target of a reference is always a row in a 
typed table or a typed view. When a reference type is used, it may have a 
scope defined. 
10.5  User defined functions
DB2 UDB provides feature for creating additional functions, which can be used 
as utilities or a methods on existing data types. This provides you the capability 
to extend and customize your SQL according to your requirements. They can be 
invoked in same way as your built in DB2 UDB functions. 
Another main advantage of using UDF is it allows you to perform your logic inside 
the DB2 UDB server. By this way you can pass some of your application logic to 
server side for faster execution. Also, DB2 UDB supports implementation of 
these user defined functions in SQL or number of external programming 
languages. This provides you a feature to use the power of languages like C, 
C++, Java, OLE, etc. 
The UDF can be of the types:
Scalar function
A scalar function is a user defined function, which returns only single values 
all the time. They are quite useful while writing a utility functions based on 
existing SQL functions. A scalar function can be referenced in the same 
contexts as any built in function.
A scalar function can be sourced or external. A sourced function is defined to 
the database with a reference to another built in or user defined function, 
whereas an external function is defined to the database with a reference to an 
external library or code. Example 10 7 shows both source and external 
creation for the function 
stringId, 
which ID type to varchar(20).
Example 10 7   Scalar functions
db2>create function stringId(ID) returns varchar(20) source DIGITS(INTEGER)
db2>create function stringId(ID) returns varchar(10) external name  itso!id  
language C parameter style SQL deterministic no SQL no external action
Column function
A column function is a user defined function which single valued answers 
from a set of like values. They are quite useful when you want to aggregate a 
result from set of rows. Currently, only sourced column functions are 
supported in DB2 UDB. It means you can create a column function sourced 
upon one of the built in column functions, and you cannot write a column 
 Chapter 10. Advanced DB2 UDB features 
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