- Predicate pushdown now splits AND predicates and pushes each to
the correct side of the join (left table vs right table)
- FROM clause no longer duplicates tables that appear in JOINs
- Constant folding no longer mangles date literals (skips strings)
- Cost model: hash join uses build/probe costs, nested_loop uses
per-row probe cost instead of cartesian product
- Physical operator selection defaults to hash join for medium+ tables
- Two-pass SQL generation: collect join tables first, then emit FROM
- Demo shows 86% cost reduction on users/orders query, 25% on
departments/employees query from ekeric13/sql-query-optimization-guide
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