Complex Patterns

Concepts: dmJunctionTables

The Many-to-Many Fan-Out Problem When you join through a many-to-many relationship, your row count explodes. If a product belongs to 3 categories and has 10 orders, joining products to categories to orders produces 30 rows instead of 10. This is the fan-out trap, and it silently inflates every SUM, COUNT, and AVG downstream. The fix is to pre-aggregate before joining, or to use a bridge table with weighting factors that sum to 1.0 per entity. This is covered in depth in the Bridge Tables lesson. Ternary Relationships Some relationships involve three entities simultaneously. A supplier provides a specific part to a specific project. The relationship is not between any two entities alone. It is between all three at once. Modeling this requires a three-column junction table. The junction tabl