After the Analyze stage from 1.2.2, the raw parse tree has become a Query tree. This section is about the shape of that result. How it differs from a raw parse tree, what abstraction sits at its core, and what assumptions the next stages (rewriter and planner) get to start from when they receive a Query tree.

Tokens descend into catalog coordinates

A raw parse tree and a Query tree are both trees, but they sit on different planes. A raw parse tree mirrors the syntactic structure of SQL text, so its nodes look a lot like tokens. Where a table name appeared, you find a node carrying that name as a token. Where a column appeared, you find another name token. The types of expressions are not yet determined.

A Query tree is what those tokens look like after they have been resolved against the catalog. The same positions hold different representations now. Where a table name was, there is now an RTE carrying that table's OID and lock mode.…