MUTATING ERROR IN TRIGGERS

MUTATING_ERROR:
                 Either insert or update or delete or select any two operations perform on same table at the same time in trigger,at that time mutating error will be happend.

to avoid this mutating error we can use pragma autonomous_transaction.

examples of mutating error:
         example 1 :
            here we are deleting the row and at the same time we are selecting(DRL) the record then it leads to mutating error

CREATE OR REPLACE TRIGGER mut_trig
AFTER DELETE ON test 
FOR EACH ROW
DECLARE
 a VARCHAR2(10);
BEGIN
  SELECT name INTO a 
  FROM test 
  WHERE id=111;
  INSERT INTO test (id,name) VALUES (222,'VOLVO');
  DBMS_OUTPUT.PUT_LINE('NAME: '||a);
END mut_trig;
/
Trigger created.

sql>delete from test;

ERROR at line 1:
ORA-04091: table SYSTEM.TEST is mutating, trigger/function may not see it
ORA-06512: at "SYSTEM.MUT_TRIG", line 4
ORA-04088: error during execution of trigger 'SYSTEM.MUT_TRIG'

----------------------------------------------------------------------------------------------------------------
example 2:
           here we are deleting the row and at the same time we are updating(DML) the record then it leads to mutating error

CREATE OR REPLACE TRIGGER mutu_trig
AFTER DELETE ON test 
FOR EACH ROW
DECLARE
BEGIN
   UPDATE test  SET name='VOLVO'
   WHERE name='HP';
END mutu_trig;
/
Trigger created.

SQL> DELETE FROM test;
DELETE FROM test
            *
ERROR at line 1:
ORA-04091: table SYSTEM.TEST is mutating, trigger/function may not see it
ORA-06512: at "SYSTEM.MUTU_TRIG", line 3

ORA-04088: error during execution of trigger 'SYSTEM.MUTU_TRIG'
                                                                                                        
                                                                                          Gouthami.
-----------------------------------------------------------------------------------------------------