True, if 1. You start from a normalized schema. 2. You denormalize in a structured way (eg dimensional modelling), rather than any old how. 3. You test the c

True, if 1. You start from a normalized schema. 2. You denormalize in a structured way (eg dimensional modelling), rather than any old how. 3. You test the change. Database query planners work better when they can take logically-safe shortcuts in their work. In large part that comes down to a properly-constructed schema. Denormalizing makes it harder for the query planner. It also means you will probably lose out on future query planner enhancements. Generally speaking, if someone wants to denormalize, I want to know the actual business value created and that the business risk is properly understood.