Deadlock error in trigger

Question

I created the following trigger and my requirement is updating the table with status column y, if the status column null values are less
than particular number have to insert few records into the same table...here is the code..
CREATE OR REPLACE TRIGGER WMOS_TEMP.insert_rec
after UPDATE
ON RSORT_TEMP
REFERENCING NEW AS New OLD AS Old
for each row
WHEN (
new.status = 'Y'
DECLARE
null_count pls_integer;
pragma autonomous_transaction;
begin
select count(*) into null_count from rsort_temp where status is null;
dbms_output.put_line ('null_count'||null_count);
if(null_count < 2) then
INSERT INTO rsort_temp
SELECT 1,ddm.dock_door_brcd, ah.SHPMT_NBR, ch.case_nbr,NULL
FROM case ch, asn ah, master ddm
WHERE ch.ORIG_NBR = ah.SHPMT_NBR
AND ch.ORIG_NBR = ddm.curr_nbr
AND ah.stat_code >= 10
AND ah.stat_code <= 30
AND ch.stat_code = 0
AND SUBSTR (ddm.brcd, 1, 2) = 'DR' and rownum < 10 ;
commit;
end if;
END;
but I got the following error:
ORA-04091: table WMOS_TEMP.RECEIVEANDSORT_TEMP is mutating, trigger/function may not see it
ORA-06512: at "WMOS_TEMP.INSERT_REC", line 4
ORA-04088: error during execution of trigger 'WMOS_TEMP.INSERT_REC'
Can you tell me how to code so that my requirement got done.
Thanks,

Answer 1

Hi,
There's a lot wrong with this solution. You need to read about the mutating table error.
First, in a row-level trigger you cannot reference your own trigger table in a select, insert, update or delete, because a change is still in progress, there's no consistent picture of the data there.
Second, you can't commit transactions in a trigger, they're not an atomic part of a transaction.
The "pragma autonomous transaction" was not created to circumvent those issues, so you need to rethink your logic. You either have to put that code in a stored procedure, likely the ideal option, or you could
use the workaround with a package, and using statement level trigger with the row level to accomplish that logic (which Tom shows in his AskTom post below).
Read these texts please. There's some database fundamentals you need to grasp before you think of the best solution for this problem.
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:9579487119866
http://www.oracle.com/technology/oramag/oracle/08-sep/o58asktom.html