Understand normalization
Understand the reasons for normalization, the five most common levels of normalization, how to normalize a database to third normal form
Understand primary, foreign, and composite keys
Understand the reason for keys in a database, choose appropriate primary keys, select appropriate data type for keys, select appropriate fields for composite keys, understand the relationship between foreign and primary keys
Understand indexes
Understand clustered and non-clustered indexes and their purpose in a database