Create a Python UDx to Order a List of Values

Posted April 25, 2019 by James Knicely, Vertica Field Chief Technologist

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User-Defined Extensions (UDxs) are functions contained in external shared libraries that are developed in C++, Python, Java, or R using the Vertica SDK. The external libraries are defined in the Vertica catalog using the CREATE LIBRARY statement. They are best suited for analytic operations that are difficult to perform in SQL, or need to be performed frequently enough that their speed is a major concern.

An engineering buddy of mine, George Jen, recently wrote a cool Python UDx that will sort a string of values alphabetically. He graciously agreed to let me use it as an example showing how simple it is to create a UDx in Vertica!

Example: dbadmin=> \! cat /home/dbadmin/ import datetime import vertica_sdk class sortDelimitedString(vertica_sdk.ScalarFunction): """ """ def processBlock(self, server_interface, arg_reader, res_writer): while True: if arg_reader.isNull(0): res_writer.setNull() else: x = arg_reader.getString(0) y = arg_reader.getString(1) arr = x.split(y) arr = sorted(arr) z=y.join(arr) res_writer.setString(z) if not break class sortDelimitedString_factory(vertica_sdk.ScalarFunctionFactory): def getPrototype(self, srv_interface, arg_types, return_type): arg_types.addVarchar() arg_types.addVarchar() return_type.addVarchar() def getReturnType(self, srv_interface, arg_types, return_type): return_type.addVarchar(64000) def createScalarFunction(self, srv): return sortDelimitedString() dbadmin=> CREATE or replace LIBRARY sortDelimitedStringlib AS '/home/dbadmin/' LANGUAGE 'Python'; CREATE LIBRARY dbadmin=> CREATE or replace FUNCTION sortDelimitedString AS LANGUAGE 'Python' NAME 'sortDelimitedString_factory' LIBRARY sortDelimitedStringlib fenced; CREATE FUNCTION dbadmin=> SELECT sortDelimitedString('Z,S,A,X,C,B', ','); sortDelimitedString --------------------- A,B,C,S,X,Z (1 row) That was easy! Thanks George!

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Have fun!