SQL Error: ORA-04091 while executing Trigger - oracle

Question

I am trying to execute my trigger:
CREATE OR REPLACE TRIGGER Trg_video_bfr_delete
AFTER DELETE ON CMS_VIDEO
FOR EACH ROW
DECLARE
CODE varchar2(60);
BEGIN
SELECT CODE INTO CODE
from CMS_VIDEO
WHERE CODE = :OLD.CODE;
IF CODE IS NOT NULL THEN
INSERT INTO ASSET_DELETE_INDEX(CODE,ASSET_TYPE,IW_VPATH,LANGUAGE,MODIFIED_DTE)
VALUES (CODE,'Video',:old.IW_VPATH,:old.CONTENT_LANGUAGE,sysdate);
END IF;
EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO ASSET_DELETE_INDEX (CODE,ASSET_TYPE,IW_VPATH,LANGUAGE,MODIFIED_DTE)
VALUES (CODE,'Video',null,:old.CONTENT_LANGUAGE,sysdate);
COMMIT;
END Trg_video_bfr_delete;
/
But I am getting the following error while executing a delete command on the table
Error report -
SQL Error: ORA-04091: table LSDS.CMS_VIDEO is mutating, trigger/function may not see it
ORA-06512: at "LSDS.TRG_VIDEO_BFR_DELETE", line 6
ORA-04088: error during execution of trigger 'LSDS.TRG_VIDEO_BFR_DELETE'
04091. 00000 - "table %s.%s is mutating, trigger/function may not see it"
*Cause: A trigger (or a user defined plsql function that is referenced in
this statement) attempted to look at (or modify) a table that was
in the middle of being modified by the statement which fired it.
*Action: Rewrite the trigger (or function) so it does not read that table.
Could anyone please help?

Answer 1

You have written trigger AFTER DELETE ON CMS_VIDEO. This trigger will fire when DELETE is performed from CMS_VIDEO table. So when CMS_VIDEO table is being modified, you cannot modify or query the same table in any of your triggers, procedures or functions.
CREATE OR REPLACE TRIGGER Trg_video_bfr_delete
AFTER DELETE ON CMS_VIDEO
FOR EACH ROW
BEGIN
IF :old.CODE IS NOT NULL THEN
INSERT INTO ASSET_DELETE_INDEX(CODE, ASSET_TYPE, IW_VPATH, LANGUAGE, MODIFIED_DTE)
VALUES (:old.CODE, 'Video', :old.IW_VPATH, :old.CONTENT_LANGUAGE, sysdate);
END IF;
END Trg_video_bfr_delete;
/

Answer 2

This is because you are deleting record from table and same table is used as reference inside trigger. This is case of "Mutating Error". You should switch to statement level trigger is it fits your requirement or you can use compound trigger which has multiple entry point and are capable of handling such scenarios.
Please refer https://oracle-base.com/articles/9i/mutating-table-exceptions

Answer 3

As per the snippet provided, I dont see any point in doing a SELECT on mutating TABLE.
We can easily ise :OLD.CODE to fetch the value. Hope below snippet helps.
CREATE OR REPLACE TRIGGER Trg_video_bfr_delete AFTER
DELETE ON CMS_VIDEO FOR EACH ROW
-- DECLARE CODE VARCHAR2(60);
BEGIN
-- SELECT CODE INTO CODE FROM CMS_VIDEO WHERE CODE = :OLD.CODE;
IF CODE IS NOT NULL THEN
INSERT
INTO ASSET_DELETE_INDEX
(
CODE,
ASSET_TYPE,
IW_VPATH,
LANGUAGE,
MODIFIED_DTE
)
VALUES
(
:old.code,
'Video',
:old.IW_VPATH,
:old.CONTENT_LANGUAGE,
sysdate
);
END IF;
EXCEPTION
WHEN OTHERS THEN
INSERT
INTO ASSET_DELETE_INDEX
(
CODE,
ASSET_TYPE,
IW_VPATH,
LANGUAGE,
MODIFIED_DTE
)
VALUES
(
:old.code,
'Video',
NULL,
:old.CONTENT_LANGUAGE,
sysdate
);
COMMIT;
END Trg_video_bfr_delete;