A well designed database looks after itself. It enforces Referential Integrity so that no item may be removed while other items refer to it.
It includes Check Constraints to ensure that all data are valid according to system defined rules.
Indexes on the right columns support the best possible performance and server-side Stored Procedures provide services for client applications.
Good database design depends on a sound understanding of Relational Database principles, and knowledge of the business domain. A Logical Data Model is independent of any proprietary database type (e.g. Oracle or Sybase or MySQL or Access) and leads to a Physical Data Model for the selected type.
Good performance depends on good design and database server resources. Sizing, scalability, and type of use must all be taken into account.