Relational database constraints

The main contents of the chapter consist of the following: Function M-files, syntax of function M-Files, comments, multiple input and output functions, relational model concepts, relational model constraints and relational database schemas, update operations and dealing with constraint violations.

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In this chapter, The contents concentrate on describing the basic principles of the relational model of data, begin by defining the modeling concepts and notation of the relational model, discussion of relational constraints that are considered an important part of the relational model and are automatically enforced in most relational DBMSs, defines the update operations of the relational model,...

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Chapter 8 describes more advanced features of the SQL language standard for relational databases. In this chapter present more complex features of SQL retrieval queries, such as nested queries, joined tables, outer joins, aggregate functions, and grouping.

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The relational Model of Data is based on the concept of a Relation. A Relation is a mathematical concept based on the ideas of sets. The strength of the relational approach to data management comes from the formal foundation provided by the theory of relations. We review the essentials of the relational approach in this chapter.

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Data Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey. Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations.

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GUIDELINE 3: Relations should be designed such that their tuples will have as few NULL values as possible  Attributes that are NULL frequently could be placed in separate relations (with the primary key)  Reasons for nulls: attribute not applicable or invalid attribute value unknown (may exist) value known to exist, but unavailable

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For each weak entity type W in the ER schema with owner entity type E, create a relation R and include all simple attributes (or simple components of composite attributes) of W as attributes of R. In addition, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s). The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any.

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Used to CREATE, DROP, and ALTER the descriptions of the tables (relations) of a database...

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