In a previous post , I explored Codd's connection trap in PostgreSQL and MongoDB — the classic pitfall where joining two independent many-to-many relationships through a shared attribute produces spurious combinations that look like facts but aren't.

The example followed Codd's 1970 suppliers–parts–projects model: we know which suppliers supply which parts, and which projects use which parts, but joining through parts to derive supplier–project relationships is a relational composition — it tells us what could be true, not what is true.

Oracle Database 26ai introduces JOIN TO ONE , a SQL extension that structurally prevents this class of errors.…