Chapter 8

   

---

1:	State the three reasons why keys are important.
A1:	Keys are important for the following reasons: They ensure that each record in a table is properly identified. They help establish and enforce various types of integrity. They serve to establish table relationships.
2:	What are the four main types of keys ?
A2:	The four main types of keys are candidate , primary , foreign , and non .
3:	What is the purpose of a candidate key ?
A3:	The purpose of a candidate key is to uniquely identify a single instance of the table's subject.
4:	State four items of the Elements of a Candidate Key .
A4:	These are the Elements of a Candidate Key : It cannot be a multipart field. It must contain unique values. It cannot contain null values. Its value is not optional in whole or in part. It comprises a minimum number of fields necessary to define uniqueness. Its values must uniquely and exclusively identify each record in the table. Its value must exclusively identify the value of each field within a given record. Its value can be modified only in rare or extreme cases.
5:	True or False: A candidate key can be composed of more than one field.
A5:	True. A candidate key can be composed of more than one field.
6:	Can a table have more than one candidate key?
A6:	Yes, a table can have more than one candidate key.
7:	What is an artificial candidate key?
A7:	A field you create for the sole purpose of serving as a candidate key is known as an artificial candidate key . You create this type of key when there are no "naturally occurring" candidate keys in a table.
8:	What is the most important key you assign to a table?
A8:	The primary key is the most important key you assign to a table.
9:	Why is this key important?
A9:	It is important for the following reasons: A primary key field exclusively identifies the table throughout the database structure and helps establish relationships with other tables. A primary key value uniquely identifies a given record within a table and exclusively represents that record throughout the entire database. It also helps to guard against duplicate records.
10:	How do you establish a primary key ?
A10:	You establish a primary key by examining the table's pool of available candidate keys and then selecting one as the primary key.
11:	State four items of the Elements of a Primary Key .
A11:	These are the Elements of a Primary Key : It cannot be a multipart field. It must contain unique values. It cannot contain null values. Its value is not optional in whole or in part. It comprises a minimum number of fields necessary to define uniqueness. Its values must uniquely and exclusively identify each record in the table. Its value must exclusively identify the value of each field within a given record. Its value can be modified only in rare or extreme cases.
12:	What must you do before you finalize your selection of a primary key?
A12:	Before you finalize your selection of a primary key, you must make absolutely certain that it exclusively identifies the value of each field within a given record.
13:	What is an alternate key ?
A13:	An alternate key is a candidate key that was not chosen to serve as the primary key of the table.
14:	What do you ensure by establishing table-level integrity?
A14:	By establishing table-level integrity, you ensure the following: There are no duplicate records in a table. The primary key exclusively identifies each record in a table. Every primary key value is unique. Primary key values are not null.
15:	Why should you review the initial table structures?
A15:	You should review the initial table structures for the following reasons: To ensure that the appropriate subjects are represented in the database To make certain that the table names and table descriptions are suitable and meaningful to everyone To make certain that the field names are suitable and meaningful to everyone To verify that all the appropriate fields are assigned to each table

---

Top