Lab 12.2 Passing Parameters In and Out of Procedures

Lab 12.2 Passing Parameters In and Out of Procedures

Lab Objectives

After this Lab, you will be able to:

• Use IN and OUT Parameters with Procedures

Parameters

Parameters are the means to pass values to and from the calling environment to the server. These are the values that will be processed or returned via the execution of the procedure. There are three types of parameters: IN, OUT, and IN OUT.

Modes

Modes specify whether the parameter passed is read in or a receptacle for what comes out.

Figure 12.1 illustrates the relationship between the parameters when they are in the procedure header versus when the procedure is executed.

Formal and Actual Parameters

Formal parameters are the names specified within parentheses as part of the header of a module. Actual parameters are the valuesexpressions specified within parentheses as a parameter listwhen a call is made to the module. The formal parameter and the related actual parameter must be of the same or compatible datatypes. Table 12.1 explains the three types of parameters.

Passing of Constraints (Datatype) with Parameter ValueS

Formal parameters do not require constraints in datatypefor example, instead of specifying a constraint such as VARCHAR2(60), you just say VARCHAR2 against the parameter name in the formal parameter list. The constraint is passed with the value when a call is made.

Matching Actual and Formal Parameters

Two methods can be used to match actual and formal parameters: positional notation and named notation. Positional notation is simply association by position: The order of the parameters used when executing the procedure matches the

Table 12.1. Three Types of Parameters

order in the procedure's header exactly. Named notation is explicit association using the symbol =>.

Syntax: formal_parameter_name => argument_value

In named notation, the order does not matter. If you mix notation, list positional notation before named notation.

Default values can be used if a call to the program does not include a value in the parameter list. Note that it makes no difference which style is used; they will both function similarly.

Lab 12.2 Exercises

12.2.1 Use IN and OUT Parameters with Procedures

Create the following text file in a text editor. Run the script at a SQL*Plus session.

-- ch12_02a.sql 
CREATE OR REPLACE PROCEDURE find_sname 
  (i_student_id IN NUMBER, 
   o_first_name OUT VARCHAR2, 
   o_last_name OUT VARCHAR2) 
AS 
BEGIN 
  SELECT first_name, last_name 
    INTO o_first_name, o_last_name 
    FROM student 
   WHERE student_id = i_student_id; 
EXCEPTION 
  WHEN OTHERS 
  THEN 
    DBMS_OUTPUT.PUT_LINE('Error in finding student_id: 
      'i_student_id); 
END find_sname;

Call the find_sname script with the following anonymous block:

-- ch12_03a.sql 
DECLARE 
  v_local_first_name student.first_name%TYPE; 
  v_local_last_name student.last_name%TYPE; 
BEGIN 
  find_sname 
    (145, v_local_first_name, v_local_last_name); 
  DBMS_OUTPUT.PUT_LINE 
    ('Student 145 is: 'v_local_first_name 
     ' ' v_local_last_name'.'); 
END;

Lab 12.2 Exercise Answers

12.2.1 Answers

Lab 12.2 Self-Review Questions

In order to test your progress, you should be able to answer the following questions.

Answers appear in Appendix A , Section 12.2 .

1)	The benefits of module code are that it (check all that apply) _____ takes IN and OUT parameters. _____ can be called by many types of calling environments. _____ is stored in the database. _____ is always valid.
2)	All module code contains the following components (check all that apply): _____ Header _____ Footer _____ Declaration _____ Exception _____ Execution
3)	If a procedure has an IN parameter, then it must have an OUT parameter. _____ True _____ False
4)	Which are valid parameter definitions in the header of a parameter? (check all that apply) _____ P_LAST_NAME IN OUT VARCHAR2(20) _____ P_STUDID OUT IN NUMBER _____ P_ZIPCODE NUMBER _____ P_COURSE_COST IN NUMBER := 1095
5)	The view USER_SOURCE only contains the code of valid procedures. _____ True _____ False