Review Questions

1.	Name the most important element of a relational database and its components .
2.	Which type of table relationship associates more than one record in a given table with more than one record in another table?
3.	What type of key can be used to enforce referential integrity between two tables in a database?
4.	What are some reasons why using a spreadsheet is not a good alternative to using a large-scale database?
5.	What are some of the benefits of abstraction in an object-relational database management system?
6.	What object-relational feature of Oracle eases the transition between relational and object-relational applications?
7.	What are the three steps in the ERA process for database design?

Answers

1.	The table is the most important element of a relational database and it consists of rows and columns . A field exists at the intersection of a row and a column.
2.	A many-to-many relationship associates more than one record in a table with more than one record in another table.
3.	A foreign key can be used to enforce referential integrity between two tables.
4.	Some reasons why a spreadsheet is not a good alternative to a large-scale database are that it’s difficult to use for multiple users, it does not offer transaction control, the cells in a spreadsheet can contain any type of data, and referential integrity controls between spreadsheets are difficult to implement efficiently .
5.	In an object-relational database management system, new datatypes can be created as aggregates of existing datatypes and other new datatypes, enhancing standards adherence and reusability.
6.	Object views allow the developer to define an object-oriented structure over an existing relational database table, thus easing the transition between relational and object-relational applications.
7.	The three steps in the ERA (entities, relationships, attributes) design process are to define the entities, then define the relationships between the entities, and then define the attributes of the entities. After one pass through all three steps, one or more iterations may be necessary.

Terms to Know

abstract datatypes
associative table
column
data modeling
encapsulation
field
foreign key
inheritance
intersection table
many-to-many relationship
methods
object view
object-relational database
one-to-many relationship
one-to-one relationship
primary key
referential integrity
relation
relational database
row
table

Chapter 2: SQLPlus and iSQLPlus Basics

This chapter begins with a few formalities and definitions, and then dives right into a discussion of the different ways to run SQL commands. Then it introduces the basics of SELECT statements and how we can retrieve and display either all columns or only certain columns of a table.

You will also find out about how to make changes to the rows in a table by using insert, update, and delete statements. In the remainder of the chapter, you will explore various ways to change the structure of tables in the database as well as control the permissions on tables.

Some SQL Formalities

A database engine is the part of an RDBMS that actually stores and retrieves data to and from the data files. The database engine is not very useful unless you can send SQL (Structured Query Language) commands to it and receive the results from those SQL commands (if any).

SQL (Structured Query Language)

The industry-standard database language used to query and manipulate the data, structures, and permissions in a relational database.

Note

“SQL” is usually pronounced “sequel”, but if you refer to “S-Q-L” in a conversation with other database developers and DBAs, they will certainly know what you’re talking about!

It is also important to separate the SQL commands from the command processor itself. For example, Oracle’s SQL*Plus client tool (available on virtually any platform that the Oracle server itself runs on) has a number of other “built-in” commands that look like SQL commands, but operate only within the SQL*Plus environment; these are called SQL*Plus commands. A SQL*Plus command may actually send many SQL commands to the Oracle server.