I thought this would be simple BUT I guess not!

Question

I have two tables Master/Detail. On the detail table I have a database trigger written for insert, update or delete that updates values not the master. This works perfect. Now I add another database trigger that when the master is deleted the trigger deletes the details (ESTBOMHMST_T1). This would work perfect IF the first trigger (UPDATE_ESTBOMHMST_TOTALS ... after insert,update,delete) was not there BUT that one fires because of the delete ... this causes a mutating table error.
I have tried to understand the section in the database triggers help onsite BUT cannot get the combination of triggers working ...
Simply put I want the database trigger to delete my child details when the master header is deleted AND also (via if the UPDATE_ESTBOMHMST_TOTALS) if the detail is acted upon (updated or perhaps just one detail of many deleted) perform a calculation back to the header to update the totals.
Here is the error I and getting and the two triggers currently being used:
ORA-04091: table SDC.ESTBOMHMST is mutating, trigger/function may not see it ORA-06512: at "SDC.UPDATE_ESTBOMHMST_TOTALS", line 5 ORA-04088: error during execution of trigger 'SDC.UPDATE_ESTBOMHMST_TOTALS' ORA-06512: at "SDC.ESTBOMHMST_T1", line 4 ORA-04088: error during execution of trigger 'SDC.ESTBOMHMST_T1'
create or replace trigger "ESTBOMHMST_T1"
BEFORE
delete on "ESTBOMHMST"
for each row
begin
delete from estbomdmst where ref_no = :old.ref_no;
end;
create or replace TRIGGER "UPDATE_ESTBOMHMST_TOTALS"
AFTER INSERT OR UPDATE OR DELETE on ESTBOMDMST
declare
begin
update ESTBOMHMST set total_mat_cost =
(select sum( nvl(mat_price,nvl(mat_cost,0)) * nvl(qty_required,0) )
from ESTBOMDMST
where ESTBOMHMST.ref_no = ESTBOMDMST.ref_no);
update ESTBOMHMST set total_lab_cost =
(select sum(nvl(lab_cost,0)) from ESTBOMDMST
where ESTBOMHMST.ref_no = ESTBOMDMST.ref_no);
end;
Edited by: user2457943 on Jan 15, 2012 7:28 AM
Edited by: user2457943 on Jan 15, 2012 9:27 AM

Answer 1

Please post the details of your DB version.
Your design is flawed for several reasons.
1. The master table is not normalized. It contains rolled up detail information. A design should almost never do this in an OLTP system. Conversely, in an OLAP system the detail data does not change in real-time so there should be no need to perform real-time rollups.
2. You say 'if the detail is acted upon and detail is deleted ' - but the detail trigger code makes NO distinction between INSERT, UPDATE or DELETE operations. Worse the DML for a single detail record attempts to cause the trigger to recalculate the master data for ALL RECORDS and not just the record based on the key value for the detail record that changed. Why are you trying to recalculate summary data for detail records whose data has not changed? That is a design flaw and will never perform anyway.
3. For OLTP systems the rollups of detail data can easily be performed using standard Oracle queries, analytical functions or customized views.
4. For OLAP systems the rollups are typically done as a batch operation after or during the process of updating the master/detail records.
5. Oracle already has functionaliity to delete child records when a parent record is deleted. You create a foreign key constraint on the child that uses the clause ON DELETE CASCADE. When a parent record is deleted the child records will also be deleted. Since there will be no more parent record there will be no child records to roll up. So the entire DELETE portion of both triggers is unnecessary in any case.