Home > Articles > Data > Oracle

This chapter is from the book

LAB 3.1 Exercises

3.1.1 Make Use of PL/SQL Language Components

Now that you have the character types and the lexical units, it is equivalent to knowing the alphabet and how to spell out words.

  1. Why does PL/SQL have so many different types of characters?

    What are they used for?

  2. What would be the equivalent of a verb and a noun in English in PL/SQL? Do you speak PL/SQL?

3.1.2 Make Use of PL/SQL Variables

Variables may be used to hold a temporary value.

Syntax : <variable-name> <data type> [optional default

Variables may also be known as identifiers. There are some restrictions that you need to be familiar with:Variables must begin with a letter and may be up to 30 characters long. Consider the following example:


This example contains a list of valid identifiers:


It is important to note that the identifiers v_last_nameand V_LAST_NAME are considered identical because PL/SQL is not case sensitive.

Next, consider an example of illegal identifiers:


student ID

Identifier X+Yis illegal because it contains the "+" sign.This sign is reserved by PL/SQL to denote an addition operation, and it is referred to as a mathematical symbol. Identifier, 1st_year is illegal because it starts with a number. Finally, identifier student IDis illegal because it contains a space.

Next, consider another example:


   first&last_names VARCHAR2(30);
   first&last_names := 'TEST NAME';

In this example, you declare a variable called first&last_names. Next, you assign a value to this variable and display this value on the screen. When run, the example produces the following output:

Enter value for last_names: Elena
old  2:  first&last_names VARCHAR2(30);
new  2:  firstElena VARCHAR2(30);
Enter value for last_names: Elena
old  4:  first&last_names := 'TEST NAME';
New  4:  firstElena := 'TEST NAME';
enter value for last_names: Elena
old  5:   DBMS_OUTPUT.PUT_LINE(first&last_names);
new  5:   DBMS_OUTPUT.PUT_LINE(firstElena);
PL/SQL procedure successfully completed. 

Consider the output produced. Because there is an ampersand (&) present in the name of the variable first&last_names, the portion of the variable is considered to be a substitution variable (you learned about substitution variables in Chapter 2). In other words, the portion of the variable name after the ampersand (last_names) is treated by the PL/SQL compiler as a substitution variable. As a result, you are prompted to enter the value for the last_namesvariable every time the compiler encounters it.

It is important to realize that while this example does not produce any syntax errors, the variable first&last_names is still an invalid identifier because the ampersand character is reserved for substitution variables. To avoid this problem, change the name of the variable from first&last_names to first_and_last_names.Therefore, you should use an ampersand sign in the name of a variable only when you use it as a substitution variable in your program.


-- ch03_1a.pls
   v_name VARCHAR2(30);
   v_dob DATE; v_us_citizen BOOLEAN;
   DBMS_OUTPUT.PUT_LINE(v_name||'born on'||v_dob);
  1. If you ran the previous example in a SQL*Plus, what would be the result?

  2. Run the example and see what happens. Explain what is happening as the focus moves from one line to the next.

3.1.3 Handle PL/SQL Reserved Words

Reserved words are ones that PL/SQL saves for its own use (e.g., BEGIN, END, and SELECT).You cannot use reserved words for names of variables, literals, or user-defined exceptions.


   exception VARCHAR2(15);
   exception := 'This is a test';
  1. What would happen if you ran the preceding PL/SQL block? Would you receive an error message? If so, explain.

3.1.4 Make Use of Identifiers in PL/SQL

Take a look at the use of identifiers in the following example:


   v_var1 VARCHAR2(20);
   v_var2 VARCHAR2(6);
   v_var3 NUMBER(5,3);
   v_var1 := 'string literal';
   v_var2 := '12.345';
   v_var3 := 12.345;   
   DBMS_OUTPUT.PUT_LINE('v_var1: '||v_var1);
   DBMS_OUTPUT.PUT_LINE('v_var2: '||v_var2);
   DBMS_OUTPUT.PUT_LINE('v_var3: '||v_var3);

In this example, you declare and initialize three variables. The values that you assign to them are literals. The first two values, 'string literal' and '12.345' are string literals because they are enclosed by single quotes. The third value, 12.345, is a numeric literal. When run, the example produces the following output:

v_var1: string literal
v_var2: 12.345
v_var3: 12.345
PL/SQL procedure successfully completed. 

Consider another example that uses numeric literals:


   v_var1 NUMBER(2) := 123;
   v_var2 NUMBER(3) := 123;
   v_var3 NUMBER(5,3) := 123456.123;
   DBMS_OUTPUT.PUT_LINE('v_var1: '||v_var1);
   DBMS_OUTPUT.PUT_LINE('v_var2: '||v_var2);
   DBMS_OUTPUT.PUT_LINE('v_var3: '||v_var3);
  1. What would happen if you ran the preceding PL/SQL block?

3.1.5 Make Use3 of Anchored Data Types

The data type that you assign to a variable can be based on a database object. This is called an anchored declaration since the variable's data type is dependent on that of the underlying object. It is wise to make use of anchored data types when possible so that you do not have to update your PL/SQL when the data types of base objects change.

Syntax: <variable_name> <type attribute>%TYPE 

The type is a direct reference to a database column.


-- ch03_2a.pls
   v_name student.first_name%TYPE;
   v_grade grade.numeric_grade%TYPE;
   DBMS_OUTPUT.PUT_LINE(NVL(v_name, 'No Name ')||
   ' has grade of '||NVL(v_grade, 0));
  1. In the previous example, what has been declared? State the data type and value.

3.1.6 Declare and Initialize Variables

In PL/SQL, variables must be declared in order to be referenced.This is done in the initial declarative section of a PL/SQL block. Remember that each declaration must be terminated with a semicolon.Variables can be assigned using the assignment operator ":=". If you declare a variable to be a constant, it will retain the same value throughout the block; in order to do this, you must give it a value at declaration.

Type the following into a text file and run the script from a SQL*Plus session.

-- ch03_3a.pls
   v_cookies_amt NUMBER := 2;
   v_calories_per_cookie CONSTANT NUMBER := 300;
   DBMS_OUTPUT.PUT_LINE('I ate ' || v_cookies_amt ||
     ' cookies with ' || v_cookies_amt *
     v_calories_per_cookie || ' calories.');
   v_cookies_amt := 3;
   DBMS_OUTPUT.PUT_LINE('I really ate ' ||
      || ' cookies with ' || v_cookies_amt *
     v_calories_per_cookie || ' calories.');
   v_cookies_amt := v_cookies_amt + 5;
   DBMS_OUTPUT.PUT_LINE('The truth is, I actually ate '
     || v_cookies_amt || ' cookies with ' ||
   v_cookies_amt * v_calories_per_cookie
     || ' calories.');
  1. What will the output be for the preceding script? Explain what is being declared and what the value of the variable is throughout the scope of the block.


    -- ch03_3a.pls
       v_lname VARCHAR2(30);
       v_regdate DATE;
       v_pctincr CONSTANT NUMBER(4,2) := 1.50;
       v_counter NUMBER := 0;
       v_new_cost course.cost%TYPE;
       v_YorN BOOLEAN := TRUE;
  2. In the previous example, add the following expressions to the beginning of the procedure (immediately after the BEGIN in the previous example), then explain the values of the variables at the beginning and at the end of the script.

       v_counter := NVL(v_counter, 0) + 1;
       v_new_cost := 800 * v_pctincr;

    PL/SQL variables are held together with expressions and operators.An expression is a sequence of variables and literals, separated by operators.These expressions are then used to manipulate data, perform calculations, and compare data.

    Expressions are composed of a combination of operands and operators. An operand is an argument to the operator; it can be a variable, a constant, a function call.An operator is what specifies the action (+, **, /, OR, etc.).

    You can use parentheses to control the order in which Oracle evaluates an expression. Continue to add the following to your SQL script the following:

       v_counter := ((v_counter + 5)*2) / 2;
       v_new_cost := (v_new_cost * v_counter)/4; 
  3. What will the values of the variables be at the end of the script?

3.1.7 Understand the Scope of a Block, Nested Blocks, and Labels

Scope of a Variable

The scope, or existence, of structures defined in the declaration section are local to that block. The block also provides the scope for exceptions that are declared and raised. Exceptions will be covered in more detail in Chapters 7, 10, and 11.

The scope of a variable is the portion of the program in which the variable can be accessed, or where the variable is visible. It usually extends from the moment of declaration until the end of the block in which the variable was declared. The visibility of a variable is the part of the program where the variable can be accessed.

BEGIN     -- outer block
       BEGIN -- inner block
       END; -- end of inner block
END;     -- end of outer block 

Labels and Nested Blocks

Labels can be added to a block in order to improve readability and to qualify the names of elements that exist under the same name in nested blocks. The name of the block must precede the first line of executable code (either the BEGIN or DECLARE) as follows:


-- ch03_4a.pls
set serveroutput on
     DBMS_OUTPUT.PUT_LINE('The procedure
           find_stu_num has been executed.');
END find_stu_num;

The label optionally appears after END. In SQL*Plus, the first line of a PL/SQL block cannot be a label. For commenting purposes, you may alternatively use "- -" or /*, ending with */.

Blocks can be nested in the main section or in an exception handler. A nested block is a block that is placed fully within another block. This has an impact on the scope and visibility of variables. The scope of a variable in a nested block is the period when memory is being allocated for the variable and extends from the moment of declaration until the END of the nested block from which it was declared. The visibility of a variable is the part of the program where the variable can be accessed.


-- ch03_4b.pls
<< outer_block >>
  v_test NUMBER := 123;
   ('Outer Block, v_test: '||v_test);
  << inner_block >>
   v_test NUMBER := 456;
     ('Inner Block, v_test: '||v_test);
     ('Inner Block, outer_block.v_test: '||
  END inner_block;
END outer_block;

This example produces the following output:

Outer Block, v_test: 123 
Inner Block, v_test: 456 
Inner Block, outer_block.v_test: 123 
  1. If the following example were run in SQL*Plus, what do you think would be displayed?

    -- ch03_5a.pls
      e_show_exception_scope EXCEPTION;
      v_student_id NUMBER := 123;
      DBMS_OUTPUT.PUT_LINE('outer student id is '
       v_student_id VARCHAR2(8) := 125;
       DBMS_OUTPUT.PUT_LINE('inner student id is '
       RAISE e_show_exception_scope;
      WHEN e_show_exception_scope
       DBMS_OUTPUT.PUT_LINE('When am I displayed?');
       DBMS_OUTPUT.PUT_LINE('outer student id is '
  2. Now run the example and see if it produces what you expected. Explain how the focus moves from one block to another in this example.

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