ERROR HANDLING
PL/SQL implements error handling with exceptions and exception handlers. Exceptions can be associated with oracle errors or with your own user-defined errors. By using exceptions and exception handlers, you can make your PL/SQL programs robust and able to deal with both unexpected and expected errors during execution.
ERROR TYPES
Ø Compile-time errors
Ø Runtime errors
Errors that occur during the compilation phase are detected by the PL/SQL engine and reported back to the user, we have to correct them.
Runtime errors are detected by the PL/SQL runtime engine which can programmatically raise and caught by exception handlers.
Exceptions are designed for run-time error handling, rather than compile-time error handling.
HANDLING EXCEPTIONS
When exception is raised, control passes to the exception section of the block. The exception section consists of handlers for some or all of the exceptions. An exception handler contains the code that is executed when the error associated with the exception occurs, and the exception is raised.
Syntax:
EXCEPTION
When exception_name then
Sequence_of_statements;
When exception_name then
Sequence_of_statements;
When others then
Sequence_of_statements;
END;
EXCEPTION TYPES
Ø Predefined exceptions
Ø User-defined exceptions
PREDEFINED EXCEPTIONS
Oracle has predefined several exceptions that corresponds to the most common oracle errors. Like the predefined types, the identifiers of these exceptions are defined in the STANDARD package. Because of this, they are already available to the program, it is not necessary to declare them in the declarative section.
Ex1:
DECLARE
a number;
b varchar(2);
v_marks number;
cursor c is select * from student;
type t is varray(3) of varchar(2);
va t := t('a','b');
va1 t;
BEGIN
-
BEGIN
select smarks into v_marks from student where sno = 50;
EXCEPTION
when no_data_found then
dbms_output.put_line('Invalid student number');
END;
-- CURSOR_ALREADY_OPEN
BEGIN
open c;
open c;
EXCEPTION
when cursor_already_open then
dbms_output.put_line('Cursor is already opened');
END;
-- INVALID_CURSOR
BEGIN
close c;
open c;
close c;
close c;
EXCEPTION
when invalid_cursor then
dbms_output.put_line('Cursor is already closed');
END;
-- TOO_MANY_ROWS
BEGIN
select smarks into v_marks from student where sno > 1;
EXCEPTION
when too_many_rows then
dbms_output.put_line('Too many values are coming to marks variable');
END;
-- ZERO_DIVIDE
BEGIN
a := 5/0;
EXCEPTION
when zero_divide then
dbms_output.put_line('Divided by zero - invalid operation');
END;
-- VALUE_ERROR
BEGIN
b := 'saketh';
EXCEPTION
when value_error then
dbms_output.put_line('Invalid string length');
END;
-- INVALID_NUMBER
BEGIN
insert into student values('a','srinu',100);
EXCEPTION
when invalid_number then
dbms_output.put_line('Invalid number');
END;
-- SUBSCRIPT_OUTSIDE_LIMIT
BEGIN
va(4) := 'c';
EXCEPTION
when subscript_outside_limit then
dbms_output.put_line('Index is greater than the limit');
END;
-- SUBSCRIPT_BEYOND_COUNT
BEGIN
va(3) := 'c';
EXCEPTION
when subscript_beyond_count then
dbms_output.put_line('Index is greater than the count');
END;
-- COLLECTION_IS_NULL
BEGIN
va1(1) := 'a';
EXCEPTION
when collection_is_null then
dbms_output.put_line('Collection is empty');
END;
--
END;
