Tim Spann talks about user-defined functions in Hive:
When you start using Hive you may miss some of the functions you are used to from Oracle, MySQL or elsewhere. Or you might just want a profanity filter. Whatever the case you can browse our list below for a large selection of UDF libraries. You can also use the pointers listed to write your own.
The Brickhouse Collection of UDFs from Klout includes functions for collapsing multiple rows into one, generating top K lists, a distributed cache, bloom counters, JSON functions, and HBase tools.
Coming from a SQL Server background, UDFs might be something you instinctively avoid (or at least that’s the case with me). In practice, though, they’re a really good addition to the product.