Multi-level accumulation

Question

I need help!
On following tables, "Proj_Dict_Cost" is a cost list to be a dictionary,
And I want keep the accumulatative relation on "Proj_Cost". But It doesnot work
Return an Error with code -4091. Where I missed?
create table Proj_Dict_Cost (
Cost_Code varchar2(10) ,
Cost_Name Varchar2(40) ,
constraint PK_CostList
Primary key (Cost_Code)
SQL> select * from proj_dict_cost where cost_code like '02%';
COST_CODE COST_NAME
02 G0FZ9$3L7Q
0201 ?IPPPTQP>?7QSC
0202 Ih<F7Q
020201 W(R5Ih<F7Q
02020101 9f;.7=08Ih<F7Q
02020102 =(V~5%Le7=08Ih<F7Q
02020103 @)3uIh<F7Q
02020104 J)9$M<Ih<F7Q
02020105 W(R5Ih<F7Q
02020106 Ih<FD#PM7QSC
02020107 Ih<F?<2l7QSC
02020108 I9M<7Q
020202 Ih<FUP1j7QSC
020203 Ih<FWIQ/7QSC
0203 5XVJ?12l7QSC
020301 9\O_L=2b7Q
020302 ?12l2bA?7Q
020303 WjL=7Q
020304 5XUpF@9@7Q
0204 1(=(7QSC
020401 9$3LIs2i7~Nq7Q
create table Proj_Cost(
Proj_No varchar2(20) not null,
Cost_Code Varchar2(10) not null,
Cost_Real number(12,2)
check(Cost_plot>=0) ,
constraint PK_Proj_Cost primary key(Proj_No,Cost_Code) ,
constraint FK_Proj_Cost Foreign Key (Cost_Code)
references Proj_Dict_Cost(Cost_Code)
CREATE OR REPLACE TRIGGER T$PROJ_COST_IDU
BEFORE INSERT OR DELETE OR UPDATE ON PROJ_COST
FOR EACH ROW
DECLARE
PRIOR_COST_CODE VARCHAR2(8);
BEGIN
IF INSERTING OR UPDATING THEN
IF INSERTING THEN
DBMS_OUTPUT.PUT('INSERTING... ');
ELSE
DBMS_OUTPUT.PUT('UPDATING... ');
END IF;
DBMS_OUTPUT.PUT_LINE(:NEW.COST_CODE);
IF LENGTH(:NEW.COST_CODE) > 2 THEN
PRIOR_COST_CODE := SUBSTR(:NEW.COST_CODE,1,LENGTH(:NEW.COST_CODE) - 2);
BEGIN
INSERT INTO PROJ_COST ( PROJ_NO
, COST_CODE
, COST_NAME
, COST_RESEARCH
, COST_PLOT
, COST_TARGET
, COST_BUDGET
, COST_SETTLED
, COST_REAL
SELECT :NEW.PROJ_NO
, COST_CODE
, COST_NAME
, :NEW.COST_RESEARCH
, :NEW.COST_PLOT
, :NEW.COST_TARGET
, :NEW.COST_BUDGET
, :NEW.COST_SETTLED
, :NEW.COST_REAL
FROM PROJ_DICT_COST
WHERE COST_CODE = PRIOR_COST_CODE
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT('EXCEPTION (');
DBMS_OUTPUT.PUT(SQLCODE);
DBMS_OUTPUT.PUT(') RAISED: ');
DBMS_OUTPUT.PUT_LINE(SQLERRM);
DBMS_OUTPUT.PUT_LINE(PRIOR_COST_CODE);
IF SQLCODE = -1 THEN --N%74N(R;T<JxLu<~
UPDATE PROJ_COST SET
COST_RESEARCH = NVL(COST_RESEARCH,0) + NVL(:NEW.COST_RESEARCH,0)
, COST_PLOT = NVL(COST_PLOT,0) + NVL(:NEW.COST_PLOT,0)
, COST_TARGET = NVL(COST_TARGET,0) + NVL(:NEW.COST_TARGET,0)
, COST_BUDGET = NVL(COST_BUDGET,0) + NVL(:NEW.COST_BUDGET,0)
, COST_SETTLED = NVL(COST_SETTLED,0) + NVL(:NEW.COST_SETTLED,0)
, COST_REAL = NVL(COST_REAL,0) + NVL(:NEW.COST_REAL,0)
WHERE COST_CODE = PRIOR_COST_CODE;
ELSE
RAISE;
END IF;
END;
END IF;
END IF;
END;
/* ELSIF DELETING THEN
IF LENGTH(:OLD.COST_CODE) > 2 THEN
PRIOR_COST_CODE := SUBSTR(:OLD.COST_CODE,1,LENGTH(:OLD.COST_CODE) - 2);
UPDATE PROJ_COST SET
COST_RESEARCH = COST_RESEARCH - NVL(:OLD.COST_RESEARCH,0)
, COST_PLOT = COST_PLOT - NVL(:OLD.COST_PLOT,0)
, COST_TARGET = COST_TARGET - NVL(:OLD.COST_TARGET,0)
, COST_BUDGET = COST_BUDGET - NVL(:OLD.COST_BUDGET,0)
, COST_SETTLED = COST_SETTLED - NVL(:OLD.COST_SETTLED,0)
, COST_REAL = COST_REAL - NVL(:OLD.COST_REAL,0)
WHERE COST_CODE = PRIOR_COST_CODE;
END IF;
DELETE PROJ_COST WHERE COST_CODE LIKE :OLD.COST_CODE&#0124; &#0124;'__' AND LENGTH(COST_CODE) > LENGTH(:OLD.COST_CODE);
SQL> insert into proj_cost (PROJ_NO, COST_CODE,COST_NAME, COST_REAL)
2 VALUES ('E1-1', '02020101','jjjjj',1234567);
insert into proj_cost (PROJ_NO, COST_CODE,COST_NAME, COST_REAL)
ERROR at line 1:
ORA-04091: table GCMIS.PROJ_COST is mutating, trigger/function may not see it
ORA-06512: a t "GCMIS.T$PROJ_COST_IDU", line 58
ORA-04088: error during execution of trigger 'GCMIS.T$PROJ_COST_IDU'
ORA-06512: at "GCMIS.T$PROJ_COST_IDU", line 58
ORA-04088: error during execution of trigger 'GCMIS.T$PROJ_COST_IDU'

Answer 1

Your INSERT statement is against the same table as that to which the trigger is attached.
If you think about it, what will happen if you put an INSERT inside a trigger that is fired during an INSERT on the same table?
INSERT->TRIGGER
|
V
INSERT->TRIGGER
|
V
INSERT->TRIGGER
and so on, until the end of time.
Oracle traps this circumstance with the error that you're getting.
null