Julian Hyde created CALCITE-1234:
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Summary: Annotate table functions to allow pushing down project,
filter
Key: CALCITE-1234
URL: https://issues.apache.org/jira/browse/CALCITE-1234
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Assignee: Julian Hyde
In general it is not possible to push relational operators through table
functions but many table functions have properties that will allow push down:
for instance, they might preserve fields, preserve row count, return rows in
the same order. If we annotate a table function with these properties, we can
automatically push down a Filter, and so forth.
Some ideas:
* {{PreservesFieldNames}}: If an output field has the same name as an input
field, it is assumed to be the same field.
* {{PreservesRows}}: Each input row causes exactly one output row, in the same
order.
* {{FiltersRows}}: Each input row causes at most one output row, in the same
order.
* {{PreservesFieldPositions}}: The leading N columns of the output are
equivalent to the leading N columns of the input.
If {{(PreservesFieldNames or PreservesFieldPositions) and (PreservesRows or
FiltersRows)}}, it is safe to push down a Filter if all of the fields of the
predicate exist in the input.
Similarly pushing down a Project; and we can push down an Aggregate if
{{PreservesRows}}.
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