Home > Articles > Data > SQL

SQL and Data

  • Print
  • + Share This
This chapter is from the book

Lab 1.3 Exercise Answers

1.3.1 Answers

  1. What does the Student schema diagram represent?

    Answer: The Student schema diagram is a graphical representation of tables in a relational database.

A schema diagram is a useful tool during the software development lifecycle. English-like words should be used to name tables and columns so that anyone, whether developer or end-user, can look at a schema diagram and grasp the meaning of data, and the relationships among them, represented there. Developers study it to understand the design of a database, long before they put hands to keyboard to develop a system, and end-users can use it to understand how their data is stored.

  1. Does the Student schema diagram tell you where a student lives? Explain.

    Answer: No. The Student schema diagram tells you how data is organized in a relational database: the names of tables, the columns in those tables, and the relationship among them. It cannot tell you what actual data looks like. You use the SQL language to interact with a relational database to view, manipulate, and store the data in the tables.

  2. What four columns are common to all tables in the Student schema diagram?

    Answer: The four columns are created_by, created_date, modified_by, and modified_date.

Database tables are often created with columns similar to these four to create an audit trail. These columns are designed to identify who first created or last modified a row of a table and when the action occurred. You will typically find these columns only on the physical schema diagram, not on the logical model. Some of these values in the columns can be filled in automatically by writing triggers. You will see an example of a table trigger in Chapter 12, "Create, Alter, and Drop Tables." (Triggers are described in further detail in the Oracle PL/SQL Interactive Workbook by Benjamin Rosenzweig and Elena Silvestrova; Prentice Hall, 2003.)

  1. What is the primary key of the course table?

    Answer: The primary key of the course table is the column course_no.

You can identify the primary key with the "PK" symbol listed next to the column. In general a primary key uniquely identifies a row in a table, and the column or columns of the primary key are defined as NOT NULL.

  1. How many primary keys does the enrollment table have? Name the column(s).

    Answer: A table can have only one primary key. The primary key of the enrollment table consists of the two columns student_id and section_id.

As mentioned earlier, a primary key uniquely identifies a single row in a table. In the case of the enrollment table, two columns uniquely identify a row and create a composite primary key.

Looking at the schema diagram you also notice that these two columns are also foreign keys. The STUDENT_ID column is the foreign key to the STUDENT table and the SECTION_ID is the foreign key to the SECTION table. Both foreign key relationships are identifying relationships.

  1. How many foreign keys does the section table have?

    Answer: Two. The foreign keys of the section table are course_no and instructor_id.

  2. Will a foreign key column in a table accept any data value? Explain using the STUDENT and ZIPCODE tables.

    Answer: No. A foreign key must use the values of the primary key it references as its domain of values.

The ZIP column is the primary key in the ZIPCODE table. The STUDENT table references this column with the foreign key ZIP column. Only values that exist in the ZIP column of the ZIPCODE table can be valid values for the ZIP column of the STUDENT table. If you attempt to create a row or change an existing row in the STUDENT table with a zip code not found in the ZIPCODE table, the foreign key constraint on the STUDENT table will reject it.

In general, a foreign key is defined as being a column, or columns, in the child table. This column refers back to the primary key of another table, referred to as the parent table.

The primary key values are the domain of values for the foreign key column. A domain is a set of values that shows the possible values a column can have. The primary key values of the parent table are the only acceptable values that may appear in the foreign key column in the other table. (Domains are not only used in context with primary key and foreign key relationships, but can also be used for a list of values that may not be stored in a table. For example, common domains include Yes/No, Gender: Male/Female/Unknown, Weekday: Sun/Mon/Tue/Wed/Thu/Fri/Sat.)

  1. If the relationship between the zipcode and student tables were optional, what would have to change in the student table?

    Answer: The foreign key column zip in the student table would have to be defined as allowing NULL values. It is currently defined as NOT NULL. The relationship should be indicated as optional instead of mandatory as shown in Figure 1.34.

    Figure 1.34Figure 1.34 The relationships of the ZIPCODE table.

There is such an optional relationship between the INSTRUCTOR and ZIPCODE tables. All the nonnull values of ZIP in the INSTRUCTOR table must be found in the ZIPCODE table.

  1. From what domain of values (what column in what table) do you think the prerequisite column of the course table gets its values?

    Answer: From the course_no column in the course table.

In this case, the prerequisite column refers back to the course_no column, which provides the domain of values for the prerequisite column. A prerequisite is valid only if it is also a valid course number in the course table. This relationship is shown in Figure 1.35.

Figure 1.35Figure 1.35 The self-referencing relationship of the COURSE table.

  1. Explain the relationship(s) the enrollment table has to other table(s).

    Answer: The student table and the section table are the parent tables of the enrollment table. The enrollment table is one of the parent tables of the grade table.

    As shown in Figure 1.36, the relationship between the STUDENT and SECTION tables signifies a student may be enrolled in zero, one, or many sections. One individual student can be enrolled in one specific section only once, otherwise the unique combination of the two columns in the ENROLLMENT table would be violated. The combination of these two foreign key columns represents the primary key of the enrollment table.

    Figure 1.36Figure 1.36 The relationships of the ENROLLMENT table.

    The relationship of the enrollment table as the parent of the grade table shows that for an individual student and her or his enrolled section there may be zero, one, or many grades. The primary key columns of the enrollment table (student_id and section_id) are foreign keys in the grade table that become part of the grade table's composite primary key. Therefore, only enrolled students may have rows in the grade as indicated with the optional line. If a row in GRADE exists, it must be for one specific enrollment in a section for one specific student.

Note: In some cases, the foreign keys become part of a table's primary key, as in the enrollment or the GRADE table. If a composite primary key contains many columns (perhaps more than four or five), a surrogate key may be considered for simplicity. The decision to use a surrogate key is based on the database designer's understanding of how data is typically accessed by the application programs.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020