Exception refers to an exceptional event. Exception is an event that disrupts the normal flow of the program, during program execution.
Pl sql exception handling:
PL/SQL provides a mechanism to handle such exceptions so that normal flow of the program can be maintained.
Types of exceptions:
1. System-defined exceptions.
2. User-defined exceptions.
Syntax for exception handling:
DECLARE //Declaration section BEGIN //Exception section EXCEPTION WHEN ex_name1 THEN //Error handling statements WHEN ex_name2 THEN -Error handling statements WHEN Others THEN //Error handling statements END; /
DECLARE s_rollNo students.rollNo%type := 10; s_name students.name%type; s_address students.address%type; BEGIN SELECT rollNo, name, address FROM students WHERE rollNo = s_rollNo; dbms_output.put_line(s_rollNo || ' ' || s_name || ' ' || s_address); EXCEPTION WHEN no_data_found THEN dbms_output.put_line('No such student!'); WHEN others THEN dbms_output.put_line('Error!'); END; /
No such student!
Pl sql raise exception:
Database server automatically raised the exceptions in case of any internal database error. But database exceptions can also be raised explicitly by using RAISE command.
Syntax of raising an exception:
DECLARE exception_name EXCEPTION; BEGIN IF condition THEN RAISE exception_name; END IF; EXCEPTION WHEN exception_name THEN statement; END; /
Pl sql user defined exception:
The PL/SQL provides the facility to define the custom or user-defined exceptions according to the need of program. A user-defined exception must be declared and then raised explicitly, using either a RAISE statement or the procedure DBMS_STANDARD.RAISE_APPLICATION_ERROR.
Syntax for declaring a user defined exception:
DECLARE custom-exception EXCEPTION;
DECLARE s_rollNo students.rollNo%type := &ss_rollNo; s_name students.name%type; s_address students.address%type; -- user defined exception ex_invalid_rollNo EXCEPTION; BEGIN IF c_id <= 0 THEN RAISE ex_invalid_rollNo; ELSE SELECT rollNo, name, address FROM students WHERE rollNo = s_rollNo; dbms_output.put_line(s_rollNo || ' ' || s_name || ' ' || s_address); END IF; EXCEPTION WHEN ex_invalid_rollNo THEN dbms_output.put_line('rollNo must be greater than zero!'); WHEN no_data_found THEN dbms_output.put_line('No such student!'); WHEN others THEN dbms_output.put_line('Error!'); END; /
(Enter a value less than 0 for rollNo)
rollNo must be greater than zero!
Pl sql predefined exceptions list:
|ACCESS_INTO_NULL||06530||-6530||It is raised when a null object is automatically assigned a value.|
|CASE_NOT_FOUND||06592||-6592||It is raised when none of the choices in the WHEN clauses of a CASE statement is selected, and there is no ELSE clause.|
|COLLECTION_IS_NULL||06531||-6531||It is raised when a program attempts to apply collection methods other than EXISTS to an uninitialized nested table or varray, or the program attempts to assign values to the elements of an uninitialized nested table or varray.|
|DUP_VAL_ON_INDEX||00001||-1||It is raised when duplicate values are attempted to be stored in a column with unique index.|
|INVALID_CURSOR||01001||-1001||It is raised when attempts are made to make a cursor operation that is not allowed, such as closing an unopened cursor.|
|INVALID_NUMBER||01722||-1722||It is raised when the conversion of a character string into a number fails because the string does not represent a valid number.|
|LOGIN_DENIED||01017||-1017||It is raised when s program attempts to log on to the database with an invalid username or password.|
|NO_DATA_FOUND||01403||+100||It is raised when a SELECT INTO statement returns no rows.|
|NOT_LOGGED_ON||01012||-1012||It is raised when a database call is issued without being connected to the database.|
|PROGRAM_ERROR||06501||-6501||It is raised when PL/SQL has an internal problem.|
|ROWTYPE_MISMATCH||06504||-6504||It is raised when a cursor fetches value in a variable having incompatible data type.|
|SELF_IS_NULL||30625||-30625||It is raised when a member method is invoked, but the instance of the object type was not initialized.|
|STORAGE_ERROR||06500||-6500||It is raised when PL/SQL ran out of memory or memory was corrupted.|
|TOO_MANY_ROWS||01422||-1422||It is raised when s SELECT INTO statement returns more than one row.|
|VALUE_ERROR||06502||-6502||It is raised when an arithmetic, conversion, truncation, or size-constraint error occurs.|
|ZERO_DIVIDE||01476||1476||It is raised when an attempt is made to divide a number by zero.|