[From MySQL AB
No matter what they say, I dont think its true. Database experts say that 80-90% of a databases overall performance comes from the SQL code thats running against it. And I just dont buy it. Instead, I think that most of a databases performance comes from optimal design, and after that SQL code comes next. If you properly design your database, then youre way ahead of the game in terms of performance issues. Thats when well-written SQL code can glide along your design like butter on a hot skillet.
The article continues at