Paun Mihut Catalin Tema 5

Student: Paun Mihut Catalin

Master: SIMR

Anul: II

Materia: DEZVOLTAREA APLICAIILOR ORACLE

Cuprins: Section 7 ....................................................................................................................................................... 2

Section 7 Lesson 1 Handling Exceptions ................................................................................................... 2

Test Quiz: Handling Exceptions ............................................................................................................... 10

Section 7 Lesson 2 Trapping Oracle Server Exceptions........................................................................... 13

Test Quiz: Trapping Oracle Server Exceptions ........................................................................................ 24

Section 7 Lesson 3 Trapping User-Defined Exceptions ........................................................................... 28

Test Quiz: Trapping User-Defined Exceptions ........................................................................................ 34

Section 7 Lesson 4 Recognizing the Scope of Exceptions ....................................................................... 37

Test Quiz: Recognizing the Scope of Exceptions ..................................................................................... 41


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Section 7

Section 7 Lesson 1 Handling Exceptions

Vocabulary

Identify the vocabulary word for each definition below:

Exception Handler Code that defines the recovery actions to be performed when

execution-time errors occur.

Exception Occurs when an error occurs during the execution of a program that

disrupts the normal operation of the program.

Exception handling Allows clean separation of the error processing code from the

executable code so that a program can continue operating in the

presence of errors.

Exception propagating The exception reproduces itself in successive enclosing blocks until

a handler is found or there are no more blocks to search in.

Try It / Solve It

1. What happens when Oracle encounters a runtime problem while executing a PL/SQL

block?

An exception is raised and the rest of the blocks execution section is not executed.

2. What do you need to add to your PL/SQL block to address these problems?

Add an exception section that includes handlers to trap and deal with all possible

problems.

3. List three advantages of handling exceptions within a PL/SQL block.

It can protect the user from frequent repeated errors.

It can prevent data in the database from being lost or overwritten.

PL/SQL code is more readable because error-handling routines can be written in the

same block in which the error occurred.


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4. Run this PL/SQL code and then answer the questions that follow.

DECLARE

v_jobid employees.job_id%TYPE;

BEGIN

SELECT job_id

INTO v_jobid

FROM employees

WHERE department_id = 80;

END;

A. What happens when you run the block?

The block fails because there is more than one employee in department 80 and an

exception (error) is raised.

B. In your own words, explain what you can do to fix this problem.

Select a unique column for the WHERE clause (the block could still fail if the unique

value entered did not exist;

Write an exception handler to trap the error.

C. Modify the code to fix the problem. Use a TOO_MANY_ROWS exception handler.

DECLARE

v_jobid employees.job_id%TYPE;

BEGIN

SELECT job_id

INTO v_jobid

FROM employees


EXCEPTION

WHEN TOO_MANY_ROWS THEN


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DBMS_OUTPUT.PUT_LINE ('Too many rows returned from the query');

END;

D. Run your modified code. What happens this time?

The exception is successfully trapped and the message 'Too many rows returned from

the query is displayed.

5. Run the following PL/SQL block, which tries to insert a new row (with department_id =

50) into the departments table. What happens and why?

BEGIN

INSERT INTO departments (department_id, department_name,manager_id, location_id)

VALUES (50, 'A new department', 100, 1500);

DBMS_OUTPUT.PUT_LINE('The new department was inserted');

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE ('An exception has occurred.');

END;

The INSERT statement failed because department_id 50 already exists and department_id

is a unique column. The rest of the executable section was skipped, therefore the message

The new department was inserted was not displayed. The WHEN OTHERS exception

handler was executed.

6. Enter the following PL/SQL block, which tries to SELECT all the employees in a specific

department. Run it three times, using department_ids 10, 20, and 30. What happens and

why?

DECLARE

v_employee_id employees.employee_id%TYPE;


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v_last_name employees.last_name%TYPE;

BEGIN

SELECT employee_id, last_name INTO v_employee_id, v_last_name

FROM employees

WHERE department_id = ;

DBMS_OUTPUT.PUT_LINE('The SELECT was successful');

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('An exception has occurred');

END;

Using department_id = 10 is successful because there is exactly one employee in that

department, therefore the SELECT returned exactly one row.

Using department_id 20 failed because there is more than one employee in that

department.

Using department_id 30 failed because there are no employees in that department.

7. Modify your code from question 6 to add two more exception handlers to trap the

possible exceptions individually. Use NO_DATA_FOUND and TOO_MANY_ROWS. Re-

run the block three times, using 10, 20, and 30 as before. Observe the message displayed in

each case.


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DECLARE

v_employee_id employees.employee_id%TYPE;

v_last_name employees.last_name%TYPE;

BEGIN

SELECT employee_id, last_name INTO v_employee_id, v_last_name

FROM employees


DBMS_OUTPUT.PUT_LINE('The SELECT was successful');

EXCEPTION

WHEN NO_DATA_FOUND THEN

DBMS_OUTPUT.PUT_LINE('No rows were selected');


DBMS_OUTPUT.PUT_LINE('More than one row was selected');

WHEN OTHERS THEN


END;

Pentru valoarea 10 :

Pentru valoarea 20:

Pentru valoarea 30:


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8. List three guidelines for trapping exceptions.

Always add exception handlers whenever there is a possibility of an error occurring.

Handle named exceptions whenever possible, instead of using OTHERS in exception

handlers.

Test your code with different combinations of bad data to see what potential errors

arise.

Write out debugging information in your exception handlers.

Carefully consider whether each exception handler should commit the transaction, roll

it back, or let it continue.

9. Enter and run the following PL/SQL block. Explain the output. Note: the WHEN

OTHERS handler successfully handles any type of exception which occurs.

DECLARE

v_number NUMBER(2);

BEGIN

v_number := 9999;

EXCEPTION

WHEN OTHERS THEN


EN An exception has occurred because the 4-digit value 9999 is too large to be assigned to a

NUMBER(2) variable. The blocks exception section has handled the exception successfully

and displayed An exception has occurred. The exception has NOT been propagated back

to the calling environment (Application Express) which therefore reports Statement

Processed, meaning: success.

10. Modify the block in question 9 to omit the exception handler, then re-run the block.

Explain the output.

DECLARE

v_number NUMBER(2);

BEGIN


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v_number := 9999;

END;

The block does not handle the exception, which therefore propagates back to Application

Express. Application Express displays an ORA-06502: PL/SQL: numeric or value error: number

precision too large.

11. Enter and run the following code and explain the output.

DECLARE

v_number NUMBER(4);

BEGIN

v_number := 1234;

DECLARE

v_number NUMBER(4);

BEGIN

v_number := 5678;

v_number := 'A character string';

END;

EXCEPTION

WHEN OTHERS THEN


DBMS_OUTPUT.PUT_LINE('The number is: '||v_number);

END;

The inner blocks attempt to assign a character string to a NUMBER variable causes an

exception. The exception is not handled in the inner block, which therefore propagates the

exception to the outer block. The outer block successfully handles the exception.

The number 1234 (not 5678) is displayed because the inner blocks v_number is out of

scope in the outer block.


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Test Quiz: Handling Exceptions Section 1

(Answer all questions in this section)

1. Which of the following is NOT an advantage of including an exception handler in a PL/SQL block? Mark for Review

(1) Points

Avoids costly and time-consuming correction of mistakes

Prevents errors from being propagated back to the calling environment

Prevents errors from occurring (*)

Code is more readable because error-handling routines can be written in the same block in which the error occurred

Correct

2. Which of the following best describes a PL/SQL exception? Mark for Review

(1) Points

A user enters an invalid password while trying to log on to the database.

An error occurs during the execution of the block, which disrupts the normal operation of the program. (*)

The programmer forgets to declare a cursor while writing the PL/SQL code.

A compile-time error occurs because the PL/SQL code references a non-existent table.

Correct

3. Which of these exceptions can be handled by an EXCEPTION section in a PL/SQL block? Mark for Review

(1) Points

An attempt is made to divide by zero

A SELECT statement returns no rows

Any other kind of exception that can occur within the block

All of the above (*)

None of the above

Correct

4. Only one exception at a time can be raised during one execution of a PL/SQL block. True or False? Mark for Review

(1) Points

True (*)

False

Correct

5. Which of the following EXCEPTION sections is constructed correctly? (Choose three.) Mark for Review

(1) Points

(Choose all correct answers)


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EXCEPTION WHEN NO_DATA_FOUND THEN statement_1; WHEN OTHERS THEN statement_2; END;

(*)

EXCEPTION WHEN NO_DATA_FOUND THEN statement_1; WHEN NO_DATA_FOUND THEN statement_2; WHEN OTHERS THEN statement_3; END;

EXCEPTION WHEN OTHERS THEN statement_1; END;

(*)

EXCEPTION WHEN OTHERS THEN statement_1; WHEN NO_DATA_FOUND THEN statement_2; END;

EXCEPTION WHEN TOO_MANY_ROWS THEN statement_1; END;

(*)

Incorrect. Refer to Section 7 Lesson 1.

6. The following EXCEPTION section is constructed correctly. True or False?

EXCEPTION WHEN ZERO_DIVIDE OR TOO_MANY_ROWS OR NO_DATA_FOUND THEN statement_1; statement_2; WHEN OTHERS THEN statement_3; END;

Mark for Review (1) Points

True (*)

False

Correct

7. Which of the following are NOT good practice guidelines for exception handling? (Choose two.) Mark for Review

(1) Points


Handle specific named exceptions where possible, instead of relying on WHEN OTHERS.

Test your code with different combinations of data to see what potential errors can happen.

Use an exception handler whenever there is any possibility of an error occurring.

Allow exceptions to propagate back to the calling environment. (*)

Include a WHEN OTHERS handler as the first handler in the exception section. (*)


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Correct

8. Examine the following code. Why does this exception handler not follow good practice guidelines? (Choose two.)

DECLARE v_dept_name departments.department_name%TYPE; BEGIN SELECT department_name INTO v_dept_name FROM departments WHERE department_id = 75; EXCEPTION WHEN OTHERS THEN DBMS_OUTPUT.PUT_LINE('A select returned more than one row');

END;



The exception handler should COMMIT the transaction.

The exception handler should test for the named exception NO_DATA_FOUND. (*)

You should not use DBMS_OUTPUT.PUT_LINE in an exception handler.

The exception section should include a WHEN TOO_MANY_ROWS exception handler. (*)

department_id 75 does not exist in the departments table.

Correct


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Anul: II


Section 7 Lesson 2 Trapping Oracle Server Exceptions

Vocabulary


Predefined Oracle Server

Errors

Each of these has a predefined name. For example, if the error ORA-

01403 occurs when no rows are retrieved from the database in a

SELECT statement, then PL/SQL raises the predefined exception-

name NO_DATA_FOUND.

PRAGMA

EXCEPTION_INIT

Tells the compiler to associate an exception name with an Oracle

error number. That allows you to refer to any Oracle Server

exception by name and to write a specific handler for it.

SQLERRM Returns character data containing the message associated with the

error number

Non-predefined Oracle

Server Errors

Each of these has a standard Oracle error number (ORA-nnnnn) and

error message, but not a predefined name. We declare our own

names for these so that we can reference these names in the

exception section.

SQLCODE Returns the numeric value for the error code (You can assign it to a

NUMBER variable.)

Try It / Solve It

1. What are the three types of exceptions that can be handled in a PL/SQL block?

predefined Oracle errors

non-predefined Oracle errors

user-defined errors

2. What is the difference in how each of these three types of exceptions is handled in the

PL/SQL block?

predefined: Oracle has assigned a name to about 20 of the most common errors. We

reference the predefined names directly in the exception section of the block;


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non-predefined: these errors do not have names and so a name must be defined in the

declare section and associated with an Oracle error number; the name is then used in

the exception section;

user defined: these are unknown to Oracle and must be named in the declare section,

raised explicitly in the executable section and then the name used in the exception

section

3. Enter and run the following PL/SQL block. Look at the output and answer the following

questions:

DECLARE

v_number NUMBER(6,2) := 100;

v_region_id wf_world_regions.region_id%TYPE;

v_region_name wf_world_regions.region_name%TYPE;

BEGIN

SELECT region_id, region_name INTO v_region_id, v_region_name

FROM wf_world_regions

WHERE region_id = 1;

DBMS_OUTPUT.PUT_LINE('Region: ' || v_region_id ||' is: ' || v_region_name);

v_number := v_number / 0;

END;

A. What error message is displayed and why ?

Because region_id = 1 does not exist, the predefined exception NO_DATA_FOUND is

raised but is not trapped within the block. The exception is propagated back to the

calling environment (Application Express) which displays ORA-01403: no data found

B. Modify the block to handle this exception and re-run your code. Now what happens and

why?

DECLARE




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BEGIN






EXCEPTION


DBMS_OUTPUT.PUT_LINE('Select returned no rows');

END;

Now the exception is successfully trapped and the corresponding exception handler is

executed.

C. Modify the block again to change the WHERE clause to region_id = 29. Re-run the

block. Now what happens and why?

Now the SELECT executes successfully because region_id 29 exists. Block execution

continues, but the next statement attempts to divide 100 by zero and raises an

unhandled ORA-01476 exception.

D. Modify the block again to handle the latest exception and re-run your code.

DECLARE




BEGIN



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EXCEPTION


DBMS_OUTPUT.PUT_LINE('Select returned no rows');

WHEN ZERO_DIVIDE THEN

DBMS_OUTPUT.PUT_LINE('Attempt to divide by zero');

END;

4. Enter and run the following PL/SQL block. Look at the output and answer the following

questions:

DECLARE

CURSOR regions_curs IS

SELECT * FROM wf_world_regions

WHERE region_id < 20

ORDER BY region_id;

regions_rec regions_curs%ROWTYPE;

v_count NUMBER(6);

BEGIN

LOOP

FETCH regions_curs INTO regions_rec;

EXIT WHEN regions_curs%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('Region: '|| regions_rec.region_id ||' Name: ' ||

regions_rec.region_name);


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END LOOP;

CLOSE regions_curs;

SELECT COUNT(*) INTO v_count



DBMS_OUTPUT.PUT_LINE('The number of regions is: ' || v_count);

END;

A. What happens and why ?

The first FETCH fails because the cursor has not been opened. The predefined

exception INVALID_CURSOR is raised but is not trapped within the block.

B. Modify the block to handle the exception and re-run your code.

DECLARE




ORDER BY region_id;


v_count NUMBER(6);

BEGIN

LOOP



DBMS_OUTPUT.PUT_LINE('Region: '|| regions_rec.region_id ||' Name: ' ||


END LOOP;

CLOSE regions_curs;





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EXCEPTION

WHEN INVALID_CURSOR THEN

DBMS_OUTPUT.PUT_LINE('Attempt to fetch from an unopenedcursor ');

END;

C. Modify the block again to add an OPEN statement for the cursor, and re-run your code.

Now what happens and why? Remember that region_id = 1 does not exist.

DECLARE




ORDER BY region_id;


v_count NUMBER(6);

BEGIN

OPEN regions_curs;

LOOP



DBMS_OUTPUT.PUT_LINE('Region: '|| regions_rec.region_id || ' Name: ' ||


END LOOP;

CLOSE regions_curs;





EXCEPTION

WHEN INVALID_CURSOR THEN

DBMS_OUTPUT.PUT_LINE('Attempt to fetch from an unopened cursor');

END;


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The cursor loop now works fine, so execution continues to the SELECT COUNT(*)

Some students may expect this to fail because region_id 1 does not exist. But a SELECT

COUNT(*) (unlike SELECT * ) always returns exactly one row, in this case with a

value of 0.

5. Oracle Server Errors:

A. Add an exception handler to the following code to trap the following predefined Oracle

Server errors: NO_DATA_FOUND, TOO_MANY_ROWS, and DUP_VAL_ON_INDEX.

DECLARE

v_language_id wf_languages.language_id%TYPE;

v_language_name wf_languages.language_name%TYPE;

BEGIN

SELECT language_id, language_name

INTO v_language_id, v_language_name

FROM wf_languages

WHERE LOWER(language_name) LIKE ''; -- for example 'ab%'

INSERT INTO wf_languages(language_id, language_name)

VALUES(80, null);

END;

Add the following exception section:

EXCEPTION


DBMS_OUTPUT.PUT_LINE('No rows were found');



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DBMS_OUTPUT.PUT_LINE('More than one row was found');

WHEN DUP_VAL_ON_INDEX THEN

DBMS_OUTPUT.PUT_LINE('This language id already exists');

B. Test your block twice using each of the following language substrings: ba, ce. There are

several language_names beginning with Ba but none beginning with Ce.

Pentru ba%:

Pentru ce%:

C. Now test your block a third time using substring: al. There is exactly one

language_name beginning with Al. Note that language_id 80 (Arabic) already exists.

Explain the output.

The SELECT succeeds but the INSERT fails with an ORA-01400 exception because

language_name cannot be null.

D. Now (keeping the substring as al) add a non_predefined exception handler to trap the

ORA-01400 exception. Name your exception e_null_not_allowed. Rerun the code and

observe the results.

DECLARE



e_null_not_allowed EXCEPTION;

PRAGMA EXCEPTION_INIT(e_null_not_allowed, -01400);


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BEGIN



FROM wf_languages

WHERE lower(language_name) LIKE al%;


VALUES(80, null);

EXCEPTION


DBMS_OUTPUT.PUT_LINE('No rows were found');


DBMS_OUTPUT.PUT_LINE('More than one row was found');

WHEN DUP_VAL_ON_INDEX THEN

DBMS_OUTPUT.PUT_LINE('This language id already exists');

WHEN e_null_not_allowed THEN

DBMS_OUTPUT.PUT_LINE('Language name cannot be null');

END;

Extension exercise

1. In preparation for this exercise, run the following SQL statement to create an error-

logging table:

CREATE TABLE error_log (who VARCHAR2(30),

when DATE,

error_code NUMBER(6),

error_message VARCHAR2(255));

Modify your PL/SQL block from question 5 to remove the four explicit exception handlers,

replacing them with a single WHEN OTHERS handler. The handler should INSERT a row into


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the error_log table each time an exception is raised and handled. The row should consist of the

Oracle username (who), when the error was raised (when), and the SQLCODE and SQLERRM

of the exception. Test your block several times, with different data values to raise each of the

four kinds of exceptions handled in the block. Finally, SELECT from the error-logging table to

check that the rows have been inserted.

DECLARE



v_sqlcode NUMBER(5);

v_sqlerrm VARCHAR2(255);

BEGIN



FROM wf_languages

WHERE lower(language_name) LIKE '';


VALUES(80, null);

EXCEPTION

WHEN OTHERS THEN

v_sqlcode := SQLCODE;

v_sqlerrm := SQLERRM;

INSERT INTO error_log(who, when, error_code, error_message)

VALUES(USER, SYSDATE, v_sqlcode, v_sqlerrm);

END;

SELECT * FROM error_log;

Dupa mai multe verificari de coduri am mai facut un SELECT:


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Test Quiz: Trapping Oracle Server Exceptions Section 1


1. Which of the following is NOT a predefined Oracle Server error? Mark for Review

(1) Points

TOO_MANY_ROWS

ZERO_DIVIDE

DUP_VAL_ON_INDEX

NO_DATA_FOUND

e_sal_too_high EXCEPTION; (*)

Correct

2. Which of the following best describes a predefined Oracle Server error? Mark for Review

(1) Points

Is not raised automatically but must be declared and raised explicitly by the PL/SQL programmer

Is associated with an Oracle error number using PRAGMA EXCEPTION_INIT

Has a standard Oracle error number but must be declared and named by the PL/SQL programmer

Has a standard Oracle error number and a standard name which can be referenced in the EXCEPTION section (*)

Correct

3. Which kind of error can NOT be handled by PL/SQL? Mark for Review

(1) Points

Non-predefined Oracle Server errors

Syntax errors (*)

Predefined Oracle Server errors

User-defined errors

Correct

4. Examine the following code. At Line A, you want to raise an exception if the employee's manager_id is null. What kind of exception is this?

DECLARE v_mgr_id employees.manager_id%TYPE; BEGIN SELECT manager_id INTO v_mgr_id FROM employees WHERE employee_id = 100; IF v_mgr_id IS NULL THEN -- Line A END IF; ...



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A NO_DATA_FOUND exception

A non-predefined Oracle server exception

A constraint violation

A user-defined exception (*)

A predefined Oracle Server exception

Correct

5. How would you trap Oracle Server exception ORA-01403: no data found? Mark for Review

(1) Points

WHEN NO_DATA_FOUND THEN ... (*)

WHEN SQL%ROWCOUNT=0 THEN ...

WHEN NO DATA FOUND THEN ...

WHEN ORA-01403 THEN ...

Correct

6. No employees exist whose salary is less than 2000. Which exception handlers would successfully trap the exception that will be raised when the following code is executed? (Choose two.)

DECLARE v_mynum NUMBER := 10; v_count NUMBER; BEGIN SELECT COUNT(*) INTO v_count FROM employees WHERE salary < 2000; v_mynum := v_mynum / v_count; EXCEPTION ... END;



NO_DATA_FOUND

ZERO_DIVIDE (*)

SQL%ROWCOUNT = 0

OTHER

OTHERS (*)

Correct

7. What is the correct syntax to associate an exception named EXCEPNAME with the non-predefined Oracle Server error ORA-02292? Mark for Review

(1) Points

SQLCODE (-2292, excepname);

RAISE_APPLICATION_ERROR (-2292, excepname);

PRAGMA EXCEPTION_INIT (excepname, -2292) (*)


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WHEN (-2292, excepname) THEN

Correct

8. An ORA-1400 exception is raised if an attempt is made to insert a null value into a NOT NULL column. DEPARTMENT_ID is the primary key of the DEPARTMENTS table. What will happen when the following code is executed?

DECLARE e_not_null EXCEPTION; BEGIN PRAGMA EXCEPTION_INIT(e_not_null, -1400); INSERT INTO departments (department_id, department_name)

VALUES(null, 'Marketing'); EXCEPTION WHEN e_not_null THEN DBMS_OUTPUT.PUT_LINE('Cannot be null'); END;


The code will not execute because the syntax of PRAGMA EXCEPTION_INIT is wrong.

The code will not execute because the syntax of the INSERT statement is wrong.

The exception will be raised and "Cannot be null" will be displayed.

The code will not execute because PRAGMA EXCEPTION_INIT must be coded in the DECLARE section. (*)

Correct

9. Examine the following code. The UPDATE statement will raise an ORA-02291 exception.

BEGIN UPDATE employees SET department_id = 45; EXCEPTION WHEN OTHERS THEN INSERT INTO error_log_table VALUES (SQLCODE); END;

What will happen when this code is executed?


The code will fail because we cannot use functions like SQLCODE directly in a SQL statement. (*)

The code will fail because we access error message numbers by using SQLERRNUM, not SQLCODE.

The code will fail because SQLCODE has not been declared.

The code will execute and insert error number 02291 into error_log_table.

Correct

10. Which type of exception MUST be explicitly raised by the PL/SQL programmer? Mark for Review

(1) Points

User-defined exceptions (*)

Predefined Oracle server errors such as TOO_MANY_ROWS

Non-predefined Oracle server errors such as ORA-01203


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All of the above

Correct

11. A PL/SQL block executes and an Oracle Server exception is raised. Which of the following contains the text message associated with the exception? Mark for Review

(1) Points

SQLERRM (*)

SQL_MESSAGE_TEXT

SQLCODE

SQL%MESSAGE

Correct

12. Which one of the following events would implicitly raise an exception? Mark for Review

(1) Points

A database constraint is violated. (*)

An UPDATE statement modifies no rows.

A SELECT statement returns exactly one row.

The PL/SQL programmer mis-spells the word BEGIN as BEGAN.

Correct


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Section 7 Lesson 3 Trapping User-Defined Exceptions

Vocabulary


RAISE_APPLICATIO

N_ERROR

A procedure used to return user-defined error messages from

stored subprograms.

RAISE Use this statement to raise a named exception.

user-defined errors These errors are not automatically rased by the Oracle Server, but

are defined by the programmer and are specific to the

programmer's code.

Try It / Solve It

All the questions in this exercise use a copy of the employees table. Create this copy by running

the following SQL statement:

CREATE TABLE excep_emps AS SELECT * FROM employees;

1. Create a PL/SQL block that updates the salary of every employee to a new value of

10000 in a chosen department. Include a user-defined exception handler that handles the

condition where no rows are updated and displays a custom message. Also include an

exception handler that will trap any other possible error condition and display the

corresponding SQLCODE and SQLERRM. Test your code three times, using

department_ids 20, 30, and 40.

DECLARE

e_no_rows_updated EXCEPTION;

BEGIN

UPDATE excep_emps

SET salary = 10000


IF SQL%NOTFOUND THEN -- sau putem spune: IF SQL%ROWCOUNT = 0

RAISE e_no_rows_updated;

END IF;

EXCEPTION


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WHEN e_no_rows_updated THEN

DBMS_OUTPUT.PUT_LINE ( 'There are no employees in that department.');

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('An error has occurred:'||SQLCODE || '-' || SQLERRM);

END;

Pentru department_id = 20:



2. Modify your code from question 2 to handle the condition where no rows are updated

using RAISE_APPLICATION_ERROR procedure in the exception section. Use an error

number of 20202. Test your code again using department_id 40 and check that the 20202

error is displayed.

DECLARE

e_no_rows_updated EXCEPTION;

BEGIN

UPDATE excep_emps

SET salary = 10000


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IF SQL%NOTFOUND THEN

RAISE e_no_rows_updated;

END IF;

EXCEPTION

WHEN e_no_rows_updated THEN

RAISE_APPLICATION_ERROR(-20202,'There are no employees in that department');

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('An error has occurred: '||SQLCODE || '-' || SQLERRM);

END;

3. Modify your code from question 3 to use RAISE_APPLICATION_ERROR in the

executable section instead of the exception section. Test your code again using

department_id 40.

DECLARE

_no_rows_updated EXCEPTION;

BEGIN

UPDATE excep_emps

SET salary = 10000


IF SQL%NOTFOUND THEN

RAISE_APPLICATION_ERROR(-20202,'There are no employees in that department');

END IF;

END;

4. Before starting this question, disable Autocommit in Application Express.

A. Enter and run the following PL/SQL block using department_id = 40, and explain the

output.

DECLARE

v_dept_id excep_emps.department_id%TYPE;


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v_count NUMBER;

BEGIN

v_dept_id := 40;


FROM excep_emps

WHERE department_id = v_dept_id;

DBMS_OUTPUT.PUT_LINE('There are ' || v_count || ' employees');

DELETE FROM excep_emps


DBMS_OUTPUT.PUT_LINE(SQL%ROWCOUNT ||' employees were deleted');

ROLLBACK;

END;

Both the SELECT and the DELETE execute successfully (no exceptions are raised) although

there are no employees in department 40.

B. Modify your block to include two user-defined exception handlers, one to test whether

SELECT returns a value of 0, and the other to test if no rows were DELETEd. Declare the

exceptions and RAISE them explicitly before trapping them in the exception section. Do

NOT use RAISE_APPLICATION_ERROR. Test your modified block using

department_id 40.

DECLARE


v_count NUMBER;

e_no_emps_in_dept EXCEPTION;

e_no_rows_deleted EXCEPTION;

BEGIN

v_dept_id := 40;


Master: SIMR

Anul: II



FROM excep_emps


IF v_count = 0 THEN

RAISE e_no_emps_in_dept;

END IF;




IF SQL%NOTFOUND THEN -- or IF SQL%ROWCOUNT = 0 THEN

RAISE e_no_rows_deleted;

END IF;


ROLLBACK;

EXCEPTION

WHEN e_no_emps_in_dept THEN

DBMS_OUTPUT.PUT_LINE('This department has no employees');

WHEN e_no_rows_deleted THEN

DBMS_OUTPUT.PUT_LINE('No employees were deleted');

END;

C. Modify your block again to use RAISE_APPLICATION_ERROR in the executable

section. Use error numbers 20203 and 20204. Test your modified block using

department_id 40.

DECLARE


v_count NUMBER;

BEGIN


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v_dept_id := 40;


FROM excep_emps


IF v_count = 0 THEN

RAISE_APPLICATION_ERROR(-20203,'This department has no employees');

END IF;




IF SQL%NOTFOUND THEN -- sau IF SQL%ROWCOUNT = 0 THEN

RAISE_APPLICATION_ERROR(-20204,'No employees were deleted');

END IF;


ROLLBACK;

END;


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Test Quiz: Trapping User-Defined Exceptions Section 1


1. What is a user-defined exception? Mark for Review

(1) Points

A predefined Oracle server exception such as NO_DATA_FOUND.

An exception which has a predefined Oracle error number but no predefined name.

An exception which is not raised automatically by the Oracle server, but must be

declared and raised explicitly by the PL/SQL programmer. (*)

An exception handler which the user (the programmer) includes in the EXCEPTION section.

Correct

2. What is the datatype of a user-defined exception? Mark for Review

(1) Points

BOOLEAN

VARCHAR2

EXCEPTION (*)

NUMBER

None of the above

Correct

3. What is wrong with the following code?

BEGIN UPDATE employees SET salary = 20000 WHERE job_id = 'CLERK'; IF SQL%ROWCOUNT = 0 THEN RAISE NO_DATA_FOUND; -- Line A END IF; EXCEPTION WHEN NO_DATA_FOUND THEN DBMS_OUTPUT.PUT_LINE('No employee was updated'); END;


Line A should be: HANDLE NO_DATA_FOUND

You cannot use SQL%ROWCOUNT in conditional control statements such as IF or CASE.

Nothing is wrong; the code will execute correctly. (*)

NO_DATA_FOUND has not been DECLAREd.

You cannot explicitly raise predefined Oracle Server errors such as NO_DATA_FOUND.

Correct

4. What will be displayed when the following code is executed? Mark for Review


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DECLARE e_myexcep EXCEPTION; BEGIN DBMS_OUTPUT.PUT_LINE('Message 1'); RAISE e_myexcep; DBMS_OUTPUT.PUT_LINE('Message 2'); EXCEPTION WHEN e_myexcep THEN DBMS_OUTPUT.PUT_LINE('Message 3'); RAISE e_myexcep; DBMS_OUTPUT.PUT_LINE('Message 4'); END;

(1) Points

The code will not execute because it contains at least one syntax error.

The code will execute but will return an unhandled exception to the calling environment.

(*)

Message 1 Message 2 Message 3 Message 4

Message 1 Message 3 Message 4

Message 1 Message 3

Correct

5. The following line of code is correct. True or False? RAISE_APPLICATION_ERROR(-21001,'My error message'); Mark for Review

(1) Points

True

False (*)

Correct

6. How are user-defined exceptions raised ? Mark for Review

(1) Points

By PRAGMA EXCEPTION_INIT

By DECLARE e_my_excep EXCEPTION;

By RAISE exception_name; (*)

None of the above. They are raised automatically by the Oracle server.

Correct

7. The following three steps must be performed to use a user-defined exception: - Raise the exception - Handle the exception - Declare the exception In what sequence must these steps be performed?


The steps can be performed in any order.


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Declare, Raise, Handle (*)

Handle, Raise, Declare

Raise, Handle, Declare

Correct

8. You want to display your own error message to the user. What is the correct syntax to do this? Mark for Review

(1) Points

RAISE application_error;

RAISE_APPLICATION_ERROR('My own message', -20001);

RAISE_APPLICATION_ERROR(20001, 'My own message');

RAISE_APPLICATION_ERROR (-20001, 'My own message'); (*)

Correct


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Section 7 Lesson 4 Recognizing the Scope of Exceptions

Vocabulary


Propogation The inner block terminates unsuccessfully, and PL/SQL passes the

exception to the outer block.

Exception scope The portion of a program in which the exception is declared and is

accessible.

Try It / Solve It

1. Enter and run the following code twice, once for each of the two country_ids 5 (which

does not exist) and 672 (Antarctica, which does exist but has no currency).

DECLARE

v_country_name wf_countries.country_name%TYPE;

v_currency_code wf_countries.currency_code%TYPE;

BEGIN

DECLARE

e_no_currency EXCEPTION;

BEGIN

SELECT country_name, currency_code

INTO v_country_name, v_currency_code

FROM wf_countries

WHERE country_id = 5; -- repeat with 672

IF v_currency_code = 'NONE' THEN

RAISE e_no_currency;

END IF;

EXCEPTION


DBMS_OUTPUT.PUT_LINE('This country does not exist');

WHEN e_no_currency THEN

DBMS_OUTPUT.PUT_LINE('This country exists but has no currency');


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END;

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('Another type of error occurred');

END;

A. Explain the output. Save your code.

Country_id 5 raises NO_DATA_FOUND and This country does not exist is displayed.

Country_id 672 raises e_no_currency and This country exists but has no currency is displayed.

B. Modify the code to move the two exception handlers to the outer block. Leave the

declaration of e_no_currency in the inner block. Execute twice, again using country_ids 5

and 672. Now what happens and why? Save your code.

DECLARE



BEGIN

DECLARE


BEGIN



FROM wf_countries




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END IF;

END;

EXCEPTION





WHEN OTHERS THEN


END;

In both executions, a PLS-00201 Identifier E_NO_CURRENCY must be declared error

occurs, because e_no_currency was declared in the inner block and is therefore out of

scope in the outer block. We would expect this for country_id 672, but what about

country_id 5, which should raise a NO_DATA_FOUND? PLS-00201 is a compile-time

error. This shows that PL/SQL checks the scope of variables when compiling the code, not

when executing it. If invalid scope is detected, the code is not executed at all.

C. Modify the code again to move the declaration of e_no_currency to the outer block. Re-

execute again using country_ids 5 and 672. Now what happens and why?

DECLARE




BEGIN


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BEGIN



FROM wf_countries




END IF;

END;

EXCEPTION





WHEN OTHERS THEN


END;

Pentru country_id = 5 :

Pentru country_id = 672 :


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Test Quiz: Recognizing the Scope of Exceptions Section 1


1. Predefined Oracle Server exceptions such as NO_DATA_FOUND can be raised automatically in inner blocks and handled in outer blocks. True or False? Mark for Review

(1) Points

True (*)

False

Correct

2. Non-predefined Oracle Server errors (associated with Oracle error numbers by PRAGMA EXCEPTION_INIT) can be declared and raised in inner blocks and handled in outer blocks. True or False?


True

False (*)

Correct

3. What will happen when the following code is executed? DECLARE e_outer_excep EXCEPTION; BEGIN DECLARE e_inner_excep EXCEPTION; BEGIN RAISE e_outer_excep; END; EXCEPTION WHEN e_outer_excep THEN DBMS_OUTPUT.PUT_LINE('Outer raised'); WHEN e_inner_excep THEN DBMS_OUTPUT.PUT_LINE('Inner raised'); END;


The code will execute successfully and 'Outer Raised' will be displayed.

The code will propagate the e_outer_excep back to the calling environment (Application Express).

The code will fail to compile because e_inner_excep cannot be referenced in the outer block. (*)

The code will fail to compile because e_inner_excep was declared but never RAISEd.

Correct

4. What will happen when the following code is executed?

DECLARE e_excep1 EXCEPTION; e_excep2 EXCEPTION; BEGIN RAISE e_excep1; EXCEPTION

WHEN e_excep1 THEN BEGIN



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RAISE e_excep2; END; END;

It will compile successfully and return an unhandled e_excep2 to the calling environment. (*)

It will fail to compile because you cannot declare more than one exception in the same block.

It will fail to compile because e_excep1 is out of scope in the subblock.

It will fail to compile because you cannot have a subblock inside an exception section.

Correct

5. There are three employees in department 90. What will be displayed when this code is executed?

DECLARE v_last_name employees.last_name%TYPE; BEGIN DBMS_OUTPUT.PUT_LINE('Message 1'); BEGIN SELECT last_name INTO v_last_name FROM employees WHERE department_id = 90; DBMS_OUTPUT.PUT_LINE('Message 2'); END; DBMS_OUTPUT.PUT_LINE('Message 3'); EXCEPTION WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('Message 4'); END;


Message 1 Message 3 Message 4

Message 1 Message 4

(*)

Message 1

An unhandled exception will be propagated back to the calling environment.

None of the above

Correct

6. What will be displayed when the following code is executed?

DECLARE v_myvar NUMBER; BEGIN v_myvar := 25; DECLARE v_myvar NUMBER := 100; BEGIN outer.v_myvar := 30; v_myvar := v_myvar / 0; outer.v_myvar := 35;



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END; v_myvar := 40; EXCEPTION WHEN ZERO_DIVIDE THEN DBMS_OUTPUT.PUT_LINE(v_myvar); END;

100

30 (*)

35

25

40

Correct

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