- TableReferences struct, which holds both:
- joined_tables, and
- outer_query_refs
- JoinedTable:
- this is just a rename of the previous TableReference struct
- OuterQueryReference
- this is to distinguish from JoinedTable those cases where
e.g. a subquery refers to an outer query's table, or a CTE
refers to a previous CTE.
Both JoinedTable and OuterQueryReference can be referred to by expressions,
but only JoinedTables are considered for join ordering optimization and so
forth.
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