Rick Hillegas created DERBY-6992:
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Summary: Extend user-defined aggregates to include multi-argument
aggregators
Key: DERBY-6992
URL: https://issues.apache.org/jira/browse/DERBY-6992
Project: Derby
Issue Type: Improvement
Components: SQL
Affects Versions: 10.15.0.0
Reporter: Rick Hillegas
Right now, a user can't implement an aggregate like LISTAGG (GROUP_CONCAT)
because LISTAGG takes multiple arguments (the expression being concatenated
plus a separator character). The cleanest solution would be an Aggregator which
is phrased in terms of a tuple argument. We should check with the Java language
experts to see how far away they are from adding tuples to Java. If that
feature is a long way out, then we might need to add our own tuple abstraction
or add a series of Aggregator interfaces, one for 2 arg aggregates, one for 3
arg aggregates, and so on.
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