On Mon, Jul 19, 2010 at 4:26 PM, Mark Tozzi <[email protected]> wrote: > Hi All, > > I've been working with UDFs in hive a lot lately, usually to implement > some manner of small lookup which isn't worth the overhead of a join, > or which for some other reason is preferable as a function as a join. > This gets me into situations where I end up wanting one UDF to have > multiple return types - for example something like a geo IP look-up > would return an integer for an area code look-up or a string for a > country name look-up. It seems the two ways to handle this are to > either write a different UDF for each return type, or potentially each > look-up, or to always return a String and use the hive built in cast > function "cast(expr as <type>)" on the return value. So far I've been > favoring the second as the first seems to lead to a proliferation of > nearly identical classes, but I'm wondering if someone with more > experience in this might have a suggestion as why one might be better > than the other, or indeed if there is a third solution that I have > overlooked. > > Thanks, > > --Mark Tozzi >
The genericUDF interface allows you to define the return type based on the parameters passed it it. Thus it is more flexible then a UDF. Check out the CASE generic UDF to see how this is done.
