Julian Hyde created CALCITE-748:
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Summary: Builder for relational expressions
Key: CALCITE-748
URL: https://issues.apache.org/jira/browse/CALCITE-748
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Assignee: Julian Hyde
Creating relational expressions currently involves calling the "create" method
of the relevant sub-class of RelNode, often with a lot of obscure parameters.
This might be appropriate for someone writing a rule, but is not particularly
friendly to someone who wants to write queries using an API.
We propose instead a builder. It would have a method for each core type of
relational expression; for example a {{filter}} method that returns a Filter.
For a given type, there might be overloads that allow you more control.
Inside the builder is a factory for each operator type. Thus a builder could be
configured to create logical rels (LogicalFilter, LogicalProject) or rels of a
different convention (HiveFilter, HiveProject).
Two particular areas that the builder can help. First, it can deduce the names
and types of output columns. (You can override types, and optionally also
names, or maybe just some names, using other APIs.)
Second, it can help you build RexNode expressions. It knows the type and names
of the input, it will let you build expressions in terms of column ordinals or
names, which are easier than RexInputRefs.
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