Mutating table exception & use of a table column in where clause

Question

Hello,
I have a scenario in which I am getting a Mutating table exception in which I have a trigger using which I insert into a second table in case there is an insert in the first table or the one which is associated with the trigger .
my trigger code has this line which is causing the Mutating table exception :
BEGIN
IF INSERTING THEN
SELECT a,b INTO var_a,var_b
FROM tableA,tableB,tableC
WHERE tableC.c = :new:c
The problem is the tableC reference in my where clause is causing a Mutating table exception , but I don't see any other way in which I can get rid of it cause I need to check if new:c values exists in the table or not , can anybody suggest how I can get rid of the tableC reference in my SQL statement yet be able to check for the value of :new:C in my statement ?

Answer 1

Hopefully this demonstrates the problem , the bold portion or the where clause is where I am getting flummoxed , I need to be able to compare the new value to a column in table C but if I use tableC reference I get mutating table exception
create or replace
trigger myTrigger
after insert or delete or update on TableC
referencing old as old new as new
for each row
DECLARE val1 number; val2 CHAR(1);
BEGIN
IF INSERTING THEN
SELECT tableA.val1,tableB.val2 INTO val1,val2
FROM TableA tableA,TableB tableB
WHERE :new.val1
AND :new.val1 is not null
AND tableA.val2 = :new.val2
AND tableB.val3 = tableA.val3
AND tableC.val4 = :new.val5
INSERT INTO TableD (col1 ,
col2,
col3,
col4,
col5,
col6,
col7,
col8,
col9)
VALUES(:new.val1,
:new.val2,
:new.val3,
tableA.val1,
tableB.val2,
:new.val4,
:new.val5,
:new.val6,
:new.val7);