Exception Handling
- 1. Database Lab Swapnali Pawar Predefined & User Defined Exceptions Swapnali Pawar
- 2. • An exception is an error condition during a program execution.An error or a warning event is called an exception. • Any abnormal condition or say event that interrupts the normal flow of your program’s instructions at run time is an exception. Or in simple words you can say an exception is a run time error. • Exceptions are designed for run time error handling rather than compile time error handling. Errors that occur during compilation phase are detected by the PL/SQL compiler and reported back to the user. What is an Exception? Swapnali Pawar
- 5. There are two types of PL/SQL exceptions in Oracle database. 1. PreDefined / System-defined Exceptions 2. User-Defined Exceptions Types of Exceptions Swapnali Pawar
- 6. • System-defined exceptions are defined and maintained implicitly by the Oracle server.These exceptions are mainly defined in the Oracle STANDARD package.Whenever an exception occurs inside the program.The Oracle server matches and identifies the appropriate exception from the available set of exceptions. • System defined exceptions majorly have a negative error code and error message.These errors have a short name which is used with the exception handler. 1. System-Defined Exceptions Swapnali Pawar
- 7. Unlike System-Define Exception, User-Define Exceptions are raised explicitly in the body of the PL/SQL block i.e more specifically inside the BEGIN-END section)using the RAISE Statement. 2. User-Define Exceptions Swapnali Pawar
- 8. • If our code does not have an exception handling, then each time we execute a statement, we must verify errors in execution . • If we avoid exception handling in our code, the actual errors get missed which gives rise to some other errors. • The exception handling allows skipping multiple verifications in the code. • It provides better readability of the code by isolating the error handlers in the code Advantages Of Exception Handling Swapnali Pawar
- 9. 1. Pre-Defined Exception • system defined exceptions are thrown by default. • Some of the popular System defined exceptions are out of memory and division by zero, having names like STORAGE_ERROR and ZERO_DIVIDE respectively. Swapnali Pawar
- 10. Exception Oracle Error SQL CODE Description ACCESS_INTO_NULL ORA - 06530 -6530 This exception is raised if a null object is naturally assigned a value. CASE_NOT_FOUND ORA - 06592 -6592 This exception is raised if none of the options in theWHEN clause is chosen and there is no existence of an ELSE clause. COLLECTION_IS_NULL ORA - 06531 -6531 This exception is raised when the code tries to apply collection methods except EXISTS to a nested table or varray which is not initialized. It can also be raised if our code tries to assign values to a nested table or varray which is not initialized. DUP_VAL_ON_INDEX ORA - 00001 -1 This exception is raised if duplicate values are tried to be stored in a column that is constrained by a unique index. CURSOR_ALREADY_OP EN ORA - 06511 -6511 This exception is raised if our code tries to open an already open cursor. INVALID_CURSOR ORA - 01001 -1001 This exception is raised if we try to do some operations on cursors which are not permitted.For example, attempting to close an already closed cursor. INVALID_NUMBER ORA - 01722 -1722 This exception is raised if the conversion to a character string to a number does not pass as the string is representing an invalid number. Pre-Defined Exception Swapnali Pawar
- 11. Exception Oracle Error SQL CODE Description SYS_INVALID_ROWID ORA-01410 -1410 This exception is raised if the conversion to a character string to a universal row id does not pass as the character string is representing an invalid row id. TIMEOUT_ON_RESOUR CE ORA-00051 -51 This exception is raised if Oracle is waiting for a resource. VALUE_ERROR ORA-06502 -6502 This exception is raised if a mathematical, conversion, truncation error happens in our program. ZERO_DIVIDE ORA-01476 -1476 This exception is raised if we try to divide a number by 0. Swapnali Pawar
- 12. 1. Pre-Defined Exception Exceptions Defined by Oracle i.e System Defined Exceptions- 1 . Zero_divide 2 . value_error 3 . Invalid_Number 4 . N0_Data_Found 5 . Too_Many_Rows 6 . Dup_Val_On_Index 7 . Cursor_Already_Open 8 . Invalid_Cursor Swapnali Pawar
- 13. This Exception occurs if any number is divided by Zero . Eg- a := &a; # 16 b := &b; # 0 c := a/b; # Occurs Divide_Zero Exception 1. Zero_divide Swapnali Pawar
- 14. 2. Value_error If Value Size exceeds or if data type is mismatched then this exception occurs A Number(3):=50000; # Exceeding 4 digit so Value_Error Occurs B Number(4):=‘Swapnali’ # DataType Missmatch Value_Error Occurs Swapnali Pawar
- 15. 3. Invalid_Number This exception occurs if invalid numeric arithmetic operation is performed Eg- ‘Swapnali’+10 # Invalid Arithmetic Operation Swapnali Pawar
- 16. 4. No_Data_Found This Exception occurs if data is not found inTable N := &roll_no; Select stud_name # No_Data_Found Exception From Student Where roll_no=N; Swapnali Pawar
- 17. 5. Too_Many_Rows This exception occurs if select statement try to fetch more than 1 record. Eno := &deptno; Select ename into EmpName From employee Where deptno=Eno; If 10 records are there for select statement then select statement fetches all 10 names & are assigned to EmpName but variable EmpName takes only one at a time so too_many_rows exception occurs Swapnali Pawar
- 18. 6. Dup_Val_On_Index This exception Occurs if we try to insert duplicate value in primary key column. Eg- Create table MyFriends (id number primary key , name varchar(30)); Insert into MyFriends id values(101); Insert into MyFriends id values(101); # 10 already exist in table so Dup_Val_On_Index exception occurs Swapnali Pawar
- 19. 7. Cursor_Already_Open If you try to open cursor which is already open without closing it then Cursor_Already_Open exception occurs. Open c1; Open c1; C1 is already open thus Cursor_Already_Open exception occurs. Swapnali Pawar
- 20. 8. Invalid_Cursor If you try to open cursor which is no declared then Invalid_Cursor exception occurs. Open C1; Cursor C1 is not declared & you try to open itThus Invalid_Cursor exception occurs. Swapnali Pawar
- 21. • User-defined exceptions are declared in a package, subprogram, or within the declaration section of the PL/SQL block of code and should be assigned names. • Once an exception occurs, the natural flow of execution is halted, and then the execution points to the exception section of the PL/SQL code. • User-defined ones have to be thrown explicitly by the RAISE keyword. • Thus the exception handling helps to deal with the errors that are encountered during the run time execution and not while compiling the program. User-Defined Exception Swapnali Pawar
- 22. 1.Declare a variable of exception data type – This variable is going to take the entire burden on its shoulders. 2.Raise the Exception – This is the part where you tell the compiler about the condition which will trigger the exception. 3.Handle the exception – This is the last section where you specify what will happen when the error which you raised will trigger Steps for Exception Handling Swapnali Pawar
- 23. User-Defined Exception The developers can build their own exceptions and use them for handling errors. They can be created in the declaration part of a subprogram and can be accessed only inside that subprogram. An exception that is created at the package level can be used whenever the package is accessed. A user-defined exception can be raised by using the RAISE keyword. Syntax - Declare Exception_name Exception; Here, the exception_n is the name of the exception that we are raising. Thus we can declare an exception by giving a name followed by the EXCEPTION keyword. An exception can be declared in a similar manner like variables are declared. However, an exception is an unexpected condition and not a data item. Swapnali Pawar
- 24. Syntax for Exception Handling DECLARE << declaration section >> BEGIN <<Block of executable code>> IF conditionTHEN RAISE exception_n; END IF; EXCEPTION WHEN excp1THEN << excp1 handling block >> WHEN excp2 THEN << excp2 handling block >> ........ WHEN othersTHEN << excp2 handling block>> END; The default exception is carried out with WHEN othersTHEN. Swapnali Pawar
- 25. 1. Raise Statement 2. Raise_Application_Error Statement User-Defined Exception When predefined exceptions don’t satisfy our requirement then we define our own exception Swapnali Pawar
- 26. 1.Using Raise Statement- Exception is raised using name.This statement is used if you want to raise exception & also want to handle it. 2. Using Raise_Application_Error Statement- Exception is raised using code.This statement is used if you want to raise exception but don’t want to handle it. Swapnali Pawar User-Defined Exception
- 27. Swapnali Pawar 1.To find sum of two number: set serveroutput on; declare a int; b int; c int; begin a:=&a; b:=&b; c:=a+b; dbms_output.put_line('sum of a and b'||c); end; 2.To find greatest number among two: set serveroutput on declare a int; b int; c int; begin a:=&a; b:=&b; if(a>b) then dbms_output.put_line('a is greater'); else dbms_output.put_line('b is greater'); end if; end;
- 28. Declare a number(2); b number(2); c number(4); one_divide exception; Begin a:= &a; b:= &b; if b=1 then raise one_divide; end if ; c:= a/b; dbms_Output.put_line(c); Exception when zero_divide then dbms_output.put_line('zero_Divide'); when one_divide then dbms_output.put_line('one_divide'); when others then dbms_output.put_line(sqlerrm); End; / Swapnali Pawar
- 29. Swapnali Pawar
- 30. 2. Using Raise_Application_Error Statement- Declare vage number(10); age number:=&vage; Begin if age < 18 then Raise_Application_Error(-20008,'Age must be greater than 18 !'); end if; dbms_output.put_line(‘Voting Allowed after completing 18 years'); Exception when others then dbms_output.put_line(sqlerrm); End; / Swapnali Pawar
- 31. Swapnali Pawar
- 32. Example. CREATETABLE CITIZEN ( ID INT NOT NULL, NAMEVARCHAR (15) NOT NULL, AGE INT NOT NULL, PRIMARY KEY (ID) ); We have created the CITIZEN table with the help of the SQL statement given below. SELECT * FROM CITIZEN Swapnali Pawar Insert values to this table with SQL statements given below: INSERT INTO CITIZENVALUES (1,‘Swapnali', 26); INSERT INTO CITIZENVALUES (8,‘Rugveda', 15); INSERT INTO CITIZENVALUES (5,‘Shree', 37);
- 33. Swapnali Pawar Coding ImplementationWith Exception Handling: DECLARE citizen_id citizen.id%type; citizen_name citizen.name%type; citizen_age citizen.age%type := 9; BEGIN SELECT id, name INTO citizen_id, citizen_name FROM citizen WHERE age = citizen_age; DBMS_OUTPUT.PUT_LINE ('Citizen id is: '|| citizen_id); DBMS_OUTPUT.PUT_LINE ('Citizen name is: '|| citizen_name); EXCEPTION WHEN no_data_foundTHEN dbms_output.put_line ('No citizen detail found'); WHEN othersTHEN dbms_output.put_line ('Errors'); END; /
- 34. Swapnali Pawar
- 35. Swapnali Pawar Student Activity 1. Using Raise statement create user defined exception which raise an error if sum of 2 numbers is greater than 5000. 2. Using Raise statement create user defined exception which raise an exception if age <18 and displays ‘Your are not Allowed for Voting This Year ! ’ Message. 3. Using Raise_Application_Error statement create your own exception code for “Salary must be above 50000 for Loan Approval !” message. 4. Create table with your name .Add columns Roll_no Name Marks .Enter some records in table. Execute various queries on that table & if records are not available raise no_data_found exception.
- 36. Swapnali Pawar