PL/SQL Exception handling

PL/SQL Exception handling

ex

BEGIN
    -- first insert
    BEGIN
        Insert into myTab(ID,NAME) values (1,'name1');
    EXCEPTION 
        when DUP_VAL_ON_INDEX then
            null; -- do something or ignore the error
    END;

    -- second insert
    BEGIN
        Insert into myTab(ID,NAME) values (2,'name2');
    EXCEPTION 
        when DUP_VAL_ON_INDEX then
            null; -- do something or ignore the error
    END;
END;

There are two types of exceptions defined in PL/SQL

1. User defined exception.
2. System defined exceptions.

System defined exceptions:

System-defined exceptions are further divided into two categories:

1. Named system exceptions.
2. Unnamed system exceptions.

• Named system exceptions: They have a predefined name by the system like ACCESS_INTO_NULL, DUP_VAL_ON_INDEX, LOGIN_DENIED etc.....




NO_DATA_FOUND: It is raised WHEN a SELECT INTO statement returns no rows


                       TOO_MANY_ROWS:It is raised WHEN a SELECT INTO statement returns more than one row

                       ZERO_DIVIDE = raises exception WHEN dividing with zero

Unnamed system exceptions:Oracle doesn’t provide name for some system exceptions called unnamed system exceptions.These exceptions don’t occur frequently.These exceptions have two parts code and an associated message.
The way to handle to these exceptions is to assign name to them using Pragma EXCEPTION_INIT
Syntax:

PRAGMA EXCEPTION_INIT(exception_name, -error_number);

error_number are pre-defined and have negative integer range from -20000 to -20999.

Example:

DECLARE

   exp exception; 

   pragma exception_init (exp, -20015); 

   n int:=10; 

  

BEGIN 

   .......

            RAISE exp; 

    ........

  

EXCEPTION 

   WHEN exp THEN

      dbms_output.put_line('aaaa'); 

  

END; 

Scope rules in exception handling:

We can’t DECLARE an exception twice but we can DECLARE the same exception in two dIFferent blocks.

Exceptions DECLAREd inside a block are local to that block and globalto all its sub-blocks.

As a block can reference only local or global exceptions, enclosing blocks cannot reference exceptions DECLAREd in a sub-block.

If we reDECLARE a global exception in a sub-block, the local declaration prevails i.e. the scope of local is more.

Example:

DECLARE

   AAAAA EXCEPTION; 

   age NUMBER:=16; 

BEGIN

  

   --  sub-block BEGINs  

   DECLARE       

        

      -- this declaration prevails  

      AAAAA EXCEPTION;   

      age NUMBER:=22; 

    

   BEGIN

      IF age > 16 THEN

         RAISE AAAAA ; /* this is not handled*/ 

      END IF; 

     

   END;           

   -- sub-block ends 

  

EXCEPTION 

  -- Does not handle raised exception  

  WHEN AAAAA THEN

    DBMS_OUTPUT.PUT_LINE 

      ('Handling  AAAAA exception.'); 

    

  WHEN OTHERS THEN

    DBMS_OUTPUT.PUT_LINE 

      ('Could not recognize exception AAAAA in this scope.'); 

END; 

------------------------

LIST of Ex

Exception	Oracle Error	SQLCODE Value
ACCESS_INTO_NULL	ORA-06530	-6530
CASE_NOT_FOUND	ORA-06592	-6592
COLLECTION_IS_NULL	ORA-06531	-6531
CURSOR_ALREADY_OPEN	ORA-06511	-6511
DUP_VAL_ON_INDEX	ORA-00001	-1
INVALID_CURSOR	ORA-01001	-1001
INVALID_NUMBER	ORA-01722	-1722
LOGIN_DENIED	ORA-01017	-1017
NO_DATA_FOUND	ORA-01403	+100
NOT_LOGGED_ON	ORA-01012	-1012
PROGRAM_ERROR	ORA-06501	-6501
ROWTYPE_MISMATCH	ORA-06504	-6504
SELF_IS_NULL	ORA-30625	-30625
STORAGE_ERROR	ORA-06500	-6500
SUBSCRIPT_BEYOND_COUNT	ORA-06533	-6533
SUBSCRIPT_OUTSIDE_LIMIT	ORA-06532	-6532
SYS_INVALID_ROWID	ORA-01410	-1410
TIMEOUT_ON_RESOURCE	ORA-00051	-51
TOO_MANY_ROWS	ORA-01422	-1422
VALUE_ERROR	ORA-06502	-6502
ZERO_DIVIDE	ORA-01476	-1476

Brief descriptions of the predefined exceptions follow:

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.