User Defined Functions allows
modular programming you can create the function once, store it in the database,
and call it any number of times in your program. User Defined Functions can be
modified independently of the program source code. Similar to Stored
Procedures, Transact-SQL User Defined Functions reduce the compilation cost of
Transact-SQL code by caching the plans and reusing them for repeated
executions. This means the user-defined function does not need to be reparsed
and re-optimized with each use resulting in much faster execution times. CLR
functions offer significant performance advantage over Transact-SQL functions
for computational tasks, string manipulation, and business logic. Transact-SQL
functions are better suited for data-access intensive logic. An operation
that filters data based on some complex constraint that cannot be expressed in
a single scalar expression can be expressed as a function. The function can
then invoked in the WHERE clause to reduce the number or rows sent to the
client.
