Oracle Exceptions

Exception:

In PL/SQL, a warning or error condition is called an exception. Exceptions can be internally defined (by the run-time system) or user defined.

Exception Types:

• Predefined Oracle Server (Implicitly Raised)

• Non predefined Oracle Server (Implicitly Raised)

• User-defined (Explicitly Raised)

Predefined Oracle Server

Predefined exceptions are used to detect and handle Oracle system errors that occur internally at program run time.
An internal exception is raised implicitly whenever your PL/SQL program violates an Oracle rule or exceeds a system-dependent limit. 

Exception	Raised when ...
ACCESS_INTO_NULL	Your program attempts to assign values to the attributes of an uninitialized (atomically null) object.
CASE_NOT_FOUND	None of the choices in the WHEN clauses of a CASE statement is selected, and there is no ELSE clause.
COLLECTION_IS_NULL	Your program attempts to apply collection methods other than EXISTS to an uninitialized (atomically null) nested table or varray, or the program attempts to assign values to the elements of an uninitialized nested table or varray.
CURSOR_ALREADY_OPEN	Your program attempts to open an already open cursor. A cursor must be closed before it can be reopened. A cursor FOR loop automatically opens the cursor to which it refers. So, your program cannot open that cursor inside the loop.
DUP_VAL_ON_INDEX	Your program attempts to store duplicate values in a database column that is constrained by a unique index.
INVALID_CURSOR	Your program attempts an illegal cursor operation such as closing an unopened cursor.
INVALID_NUMBER	In a SQL statement, the conversion of a character string into a number fails because the string does not represent a valid number. (In procedural statements, VALUE_ERROR is raised.) This exception is also raised when the LIMIT-clause expression in a bulk FETCH statement does not evaluate to a positive number.
LOGIN_DENIED	Your program attempts to log on to Oracle with an invalid username and/or password.
NO_DATA_FOUND	A SELECT INTO statement returns no rows, or your program references a deleted element in a nested table or an uninitialized element in an index-by table. SQL aggregate functions such as AVG and SUM always return a value or a null. So, a SELECT INTO statement that calls an aggregate function never raises NO_DATA_FOUND. The FETCH statement is expected to return no rows eventually, so when that happens, no exception is raised.
NOT_LOGGED_ON	Your program issues a database call without being connected to Oracle.
PROGRAM_ERROR	PL/SQL has an internal problem.
ROWTYPE_MISMATCH	The host cursor variable and PL/SQL cursor variable involved in an assignment have incompatible return types. For example, when an open host cursor variable is passed to a stored subprogram, the return types of the actual and formal parameters must be compatible.
SELF_IS_NULL	Your program attempts to call a MEMBER method on a null instance. That is, the built-in parameter SELF (which is always the first parameter passed to a MEMBER method) is null.
STORAGE_ERROR	PL/SQL runs out of memory or memory has been corrupted.
SUBSCRIPT_BEYOND_COUNT	Your program references a nested table or varray element using an index number larger than the number of elements in the collection.
SUBSCRIPT_OUTSIDE_LIMIT	Your program references a nested table or varray element using an index number (-1 for example) that is outside the legal range.
SYS_INVALID_ROWID	The conversion of a character string into a universal rowid fails because the character string does not represent a valid rowid.
TIMEOUT_ON_RESOURCE	A time-out occurs while Oracle is waiting for a resource.
TOO_MANY_ROWS	A SELECT INTO statement returns more than one row.
VALUE_ERROR	An arithmetic, conversion, truncation, or size-constraint error occurs. For example, when your program selects a column value into a character variable, if the value is longer than the declared length of the variable, PL/SQL aborts the assignment and raises VALUE_ERROR. In procedural statements, VALUE_ERROR is raised if the conversion of a character string into a number fails. (In SQL statements, INVALID_NUMBER is raised.)
ZERO_DIVIDE	Your program attempts to divide a number by zero.

Exception Examples:

set feedback off

set serveroutput on

create table foo (

  a  varchar2(10),

  b  varchar2(10),

  i  number

);

insert into foo values ('xxx','yyy',1);

insert into foo values ('zzz','aaa',1);

insert into foo values ('qqq','mmm',3);

commit;

declare

  l_a foo.a%type;

  l_b foo.b%type;

begin

  select a,b into l_a, l_b from foo where i=1;

  dbms_output.put_line('a: ' || l_a || ', b: ' || l_b);

exception 

  when too_many_rows then

    dbms_output.put_line('*** Exc: too many rows');

  when no_data_found then

    dbms_output.put_line('*** Exc: no data');

end;

/

declare

  l_a foo.a%type;

  l_b foo.b%type;

begin

  select a,b into l_a, l_b from foo where i=2;

  dbms_output.put_line('a: ' || l_a || ', b: ' || l_b);

exception 

  when too_many_rows then

    dbms_output.put_line('*** Exc: too many rows');

  when no_data_found then

    dbms_output.put_line('*** Exc: no data');

end;

/

declare

  l_a foo.a%type;

  l_b foo.b%type;

begin

  select a,b into l_a, l_b from foo where i=3;

  dbms_output.put_line('a: ' || l_a || ', b: ' || l_b);

exception 

  when too_many_rows then

    dbms_output.put_line('*** Exc: too many rows');

  when no_data_found then

    dbms_output.put_line('*** Exc: no data');

end;

/

drop table foo;

PL/SQL allows developers to define their own exceptions.User can define the error/exception programically based on the business rule. This is usually done on validating some values or parameters.Even exception can be given meaningful names.

There are 3 steps to handle the User exception

1. Define Exception

We need to define the exception before we raise and handle. User Exceptions are defined using keyword EXCEPTION in declaration section of the block.

The syntax is as follows

Code :

 <exception_name> EXCEPTION ;

2. Raise the Exception

Once the exceptions are defined , they need to be raised anywhere in the body depending upon predifined logic. User exceptions are raised using the keyword RAISE.

Syntax is as shown below

Code :

RAISE <exception_name>

3. Handle the Exception.

User exception are handled in the same way predefined exceptions are handled. They are handlded in exception block using WHEN .. THEN keyword

Syntax is as shown below

Code :

WHEN <exception_name> THEN

.....

Alternately we can give user defined error code and error message for the hadled excpetion. RAISE_APPLICATION_ERROR is used for this purpose.

Its syntax is as follows.

Code :

RAISE_APPLICATION_ERROR(<error_code>, <error_message>)

Here "error_code" should be in the range of (-20000,-20999) and "error_message" is the user defined error message for the user defined exception.