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https://issues.apache.org/jira/browse/PHOENIX-538?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14378028#comment-14378028
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Rajeshbabu Chintaguntla commented on PHOENIX-538:
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Thanks [~jamestaylor] for clarifiaction.
bq. Maybe with follow up work? It'd be good to get the basic stuff in first.
FWIW, the max length, precision, scale are part of the type declaration, so
we'd get with your proposed syntax. For example: create function
power(DECIMAL(10,2), INTEGER).
I think we need to store some details about argument like isnull , isconstant,
minvalue and maxvalue(in case of constant argument) in SYSTEM.FUNCTION because
this information will be used for validating expressions passed to function.
And also length,precision and scale are not used any validation and also
duplicate function comparison so we can leave them now and if required we can
check later.
bq. That seems reasonable to have separate commands that manages the dynamic
class path. Maybe we could even punt on this initially and folks would need to
manually manage this?
You mean we can implement add jar, list jar commands as part of basic work. If
yes It's fine for me.
bq. I'd make sure you have a way of disallowing it, though, too just in case
folks don't want to allow this functionality.
Sure. I will do this as well.
> Support UDFs
> ------------
>
> Key: PHOENIX-538
> URL: https://issues.apache.org/jira/browse/PHOENIX-538
> Project: Phoenix
> Issue Type: Task
> Reporter: James Taylor
> Assignee: Rajeshbabu Chintaguntla
>
> Phoenix allows built-in functions to be added (as described
> [here](http://phoenix-hbase.blogspot.com/2013/04/how-to-add-your-own-built-in-function.html))
> with the restriction that they must be in the phoenix jar. We should improve
> on this and allow folks to declare new functions through a CREATE FUNCTION
> command like this:
> CREATE FUNCTION mdHash(anytype)
> RETURNS binary(16)
> LOCATION 'hdfs://path-to-my-jar' 'com.me.MDHashFunction'
> Since HBase supports loading jars dynamically, this would not be too
> difficult. The function implementation class would be required to extend our
> ScalarFunction base class. Here's how I could see it being implemented:
> * modify the phoenix grammar to support the new CREATE FUNCTION syntax
> * create a new UTFParseNode class to capture the parse state
> * add a new method to the MetaDataProtocol interface
> * add a new method in ConnectionQueryServices to invoke the MetaDataProtocol
> method
> * add a new method in MetaDataClient to invoke the ConnectionQueryServices
> method
> * persist functions in a new "SYSTEM.FUNCTION" table
> * add a new client-side representation to cache functions called PFunction
> * modify ColumnResolver to dynamically resolve a function in the same way we
> dynamically resolve and load a table
> * create and register a new ExpressionType called UDFExpression
> * at parse time, check for the function name in the built in list first (as
> is currently done), and if not found in the PFunction cache. If not found
> there, then use the new UDFExpression as a placeholder and have the
> ColumnResolver attempt to resolve it at compile time and throw an error if
> unsuccessful.
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