In this section, we give an overview of the schema evolution commands available in SQL, which can be used to alter a schema by adding or dropping tables, attributes, constraints, and other schema elements. This can be done while...
Category - Software
In this section, we introduce two additional features of SQL: the CREATE ASSERTION statement and the CREATE TRIGGER statement. Before discusses CREATE ASSERTION, which can be used to specify additional types of constraints that...
SQL has a number of additional features that we have not described in this chapter but that we discuss elsewhere in the book. These are as follows: we will present the following additional SQL features: various techniques for...
In SQL, three commands can be used to modify the database: INSERT, DELETE, and UPDATE. We discuss each of these in turn. The INSERT Command In its simplest form, INSERT is used to add a single tuple to a relation. We must specify...
SQL uses the terms table, row, and column for the formal relational model terms relation, tuple, and attribute, respectively. We will use the corresponding terms interchangeably. The main SQL command for data definition is the...
So far, we have discussed the characteristics of single relations. In a relational database, there will typically be many relations, and the tuples in those relations are usually related in various ways. The state of the whole...
The relational model represents the database as a collection of relations. Informally, each relation resembles a table of values or, to some extent, a flat file of records. It is called a flat file because each record has a...
Several criteria are normally used to classify DBMSs. The first is the data model on which the DBMS is based. The main data model used in many current commercial DBMSs is the relational data model. The object data model has been...
Centralized DBMSs Architecture Architectures for DBMSs have followed trends similar to those for general computer system architectures. Earlier architectures used mainframe computers to provide the main processing for all system...
A DBMS is a complex software system. In this section we discuss the types of software components that constitute a DBMS and the types of computer database system software with which the DBMS interacts. DBMS Component...
