Identify when a table violates normalization by storing facts at multiple grains.
Normalization asks one ruthless question: what does this fact depend on? 1NF: one cell, one value Repeating lists inside a cell hide relationships. Split them so each relationship can be constrained and queried. 2NF: depend on the whole key In a composite-key table, non-key fields should depend on the whole key, not one part of it. 3NF: depend on the key, not another non-key fact If plan_name determines plan_price, do not copy plan_price into every customer row as if it depended on customer_id. Practical move Normalize writes. Denormalize reads deliberately with views, marts, or cached projections.
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