How Snowflake’s RELY Constraint Supercharges Your Star‑Schema Queries

Snowflake’s RELY constraint is a powerful but under‑used hint that tells the optimizer it can trust your primary keys and foreign keys and use them to eliminate unnecessary work—especially redundant joins. In this post, I’ll explain what RELY does, how it helps with join elimination, and walk you through concrete examples you can adapt for your own schemas. Why this matters to a data engineer? If you’ve ever used wide, reusable models with hundreds of columns designed as a single source of truth, you know how easily queries can accumulate unnecessary joins. RELY helps here by letting Snowflake eliminate redundant joins when they’re logically not needed, so queries only scan the tables that actually contribute to the result. In Snowflake, UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints on standard tables are not enforced by default; they are mainly metadata for humans and tools. However, Snowflake lets you add a RELY property on those constraints to signal: I guarantee this constraint