Merge Schema Validation (Runtime)

Overview

Gold layer merge scripts must align perfectly with DDL-defined schemas. Mismatches between source DataFrame columns and target table schemas cause 59% of Gold layer bugs. This skill provides runtime validation patterns to catch schema issues before deployment.

Key Principle: DDL (setup script) is the runtime source of truth, not YAML design specifications.

Companion skill: For design-time cross-validation of YAML ↔ ERD ↔ Lineage, see design-workers/07-design-validation/SKILL.md.

When to Use This Skill

• Creating Gold layer merge scripts (Silver → Gold)
• Ensuring DataFrame columns match target table schemas
• Validating column mappings before MERGE operations
• Debugging UNRESOLVED_COLUMN errors in merge operations
• Running pre-deployment schema validation

Core Problem: Three Sources of Truth