Abstract: Deductive engineering database （DEDB）, which integrates the engineering database （EDB）, and the deductive database （DDB）, has powerful abilities of DDB’s query and EDB’s modeling of engineering data, objects and environment. These abilities are very important for the progress of the database technology. The research and problem in relational fields are analyzed and as a result the idea of DEDB is proposed. The characteristics and shortcomings of the present database language are introduced. Then the method is discussed on how to expand SQL to support manipulating knowledge under EDB environment based on logic to ensure the language DEL is easy to use and combine with the EDB. Furthermore, the DEL’s grammar, the implementation and the instances are provided to verify the DEL SQL’s validity and applicability.