Mutating tirgger issue while setting a value

Question

I have a table and records as below:
CREATE TABLE set_time
NUM NUMBER,
ID NUMBER,
SET_VALUE CHAR(1 BYTE),
D_TIME DATE
Insert into SET_TIME (NUM, ID) Values (1, 1);
Insert into SET_TIME (NUM, ID) Values (2, 1);
Insert into SET_TIME (NUM, ID) Values (3, 1);
Insert into SET_TIME (NUM, ID) Values (4, 1);
Insert into SET_TIME (NUM, ID) Values (5, 1);
Insert into SET_TIME (NUM, ID) Values (1, 2);
Insert into SET_TIME (NUM, ID) Values (2, 2);
Insert into SET_TIME (NUM, ID) Values (3, 2);
I need a trigger,whenever all the set_values for a particular id is set to 'Y', I need to update the column d_time as sys_date.For that I wrote below trigger
CREATE OR REPLACE TRIGGER set_time_trigger
before update
ON set_time for each row
DECLARE
v_count number;
BEGIN
if :new.set_value = 'Y' then
select 1 into v_count
from dual
where exists ( select null
from set_time
where ID = :new.id
AND ( set_value != 'Y'));
if v_count is null then
update set_time
set d_time = sysdate where ID =:new.id;
end if;
end if;
end;
But while executing the below statement:
update set_time set set_value ='Y' where id = 1;
I am gettign the follwoing error:
ORA-04091: table SET_TIME is mutating, trigger/function may not see it
ORA-06512: at "SET_TIME_TRIGGER", line 13
ORA-04088: error during execution of trigger 'SET_TIME_TRIGGER'
Is there anyway that I can achieve this?. I am using Oracle 11G.
Thanks in Advance

Answer 1

1) If D_TIME depends on the data that is set for multiple rows in your table, you have a normalization problem. It sounds like you need to rethink your data model and break out the ID column into a separate table.
2) A row-level trigger cannot generally query the table on which it is defined. So you generally cannot code a row-level trigger that would query the data in other rows of the table. You could define a package which had a collection of ID values, create a before update statement-level trigger that initialized the collection, create a row-level trigger that inserted the :new.id into this packaged collection, and create an after update statement-level trigger that read the data from the collection, queried the table, and did the updates as appropriate. That's a lot of work to go through and a lot of complexity to introduce.
Additionally, this sort of trigger-based approach does not generally work in a multiuser environment. If Session A is inserting a new row with an ID of 1 and a SET_TIME of N at the same time that Session B is setting the SET_TIME of all the committed rows with an ID of 1 to Y, the trigger in Session B can update the D_TIME before session A commits its data leaving you with a case where D_TIME is set and not every row with an ID of 1 has a SET_TIME of Y.
Justin