Avoiding SQL Ambiguities caused by JOIN USING and NATURAL JOIN

SQL's NATURAL JOIN and JOIN USING syntax can introduce subtle bugs when schemas evolve. NATURAL JOIN joins on all shared column names, which is dangerous when audit columns like LAST_UPDATE exist across tables. JOIN USING is cleaner for ad-hoc queries but can break silently when new columns are added — for example, adding a column to one table can create ambiguity in a subsequent JOIN USING clause, causing errors in PostgreSQL and Oracle. The safe alternative for production queries is always JOIN ... ON with explicit table-qualified column references.