[CALCITE-1234] Annotate table functions to allow pushing down project, filter

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Julian Hyde
• Created: 10/May/16 21:52
• Updated: 27/Feb/24 22:23

Description

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.

Issue Links

• links to: GitHub Pull Request #24