User-defined functions (UDFs)
User-defined functions (frequently abbreviated as UDFs) let you code your own application logic for processing column values during an Impala query. For example, a UDF could perform calculations using an external math library, combine several column values into one, do geospatial calculations, or other kinds of tests and transformations that are outside the scope of the built-in SQL operators and functions.
You can use UDFs to simplify query logic when producing reports, or to transform data in
flexible ways when copying from one table to another with the INSERT ...
SELECT syntax.
You might be familiar with this feature from other database products, under names such as stored functions or stored routines.
Impala support for UDFs is available in Impala 1.2 and higher:
- In Impala 1.1, using UDFs in a query required using the Hive shell. (Because Impala and Hive share the same metastore database, you could switch to Hive to run just those queries requiring UDFs, then switch back to Impala.)
- Starting in Impala 1.2, Impala can run both high-performance native code UDFs written in C++, and Java-based Hive UDFs that you might already have written.
- Impala can run scalar UDFs that return a single value for each row of the result set, and user-defined aggregate functions (UDAFs) that return a value based on a set of rows. Currently, Impala does not support user-defined table functions (UDTFs) or window functions.
