I am trying to run a stored procedure, but i am getting errors. So thought of checking part of code
This is code i ran to check but getting some errors
Can anyone please help

EXECUTE IMMEDIATE 'Alter Session Enable Parallel DML';

INSERT /*+ APPEND*/ INTO DWSGDW01.DWT00050_IMC_CCYYMM_FACT (
SNAP_MO_YR_KEY_NO
, IMC_KEY_NO
, IMC_AFF_KEY_NO
, IMC_CNTRY_KEY_NO
, IMC_DERIVED_NM
, IMC_ST_PROV_CD
, IMC_POSTL_CD
, IMC_TYPE_CD
, ENGAGE_FLG
, IMC_CURR_SEG_KEY_NO
, IMC_APPL_DT_KEY_NO
, LAST_RENEW_DT_KEY_NO
, IMC_DLETE_DT_KEY_NO
, SPON_IMC_KEY_NO
, IMC_CLASS_CD
, IMC_HIGH_AWD_KEY_NO
, IMC_ACHV_AWD_KEY_NO
, IMC_CURR_QUAL_AWD_KEY_NO
, IMC_ISPON_FLG
, IMC_ISPON_AFF_ID
, IMC_LANG_CD
, IMC_ISPON_IMC_KEY_NO
, IMC_EXPIRE_DT_KEY_NO
, FRONTLINE_CNT
, LOM_DY_NO
, LOA_KEY_NO
, GLOBL_IMC_TYPE_KEY_NO
, POSTL_CD_KEY_NO
, STATUS_KEY_NO
, LAST_ORD_OIMC_DT_KEY_NO
, LAST_ORD_VIMC_DT_KEY_NO
, LAST_SPON_DT_KEY_NO
, LAST_UPDT_DT_KEY_NO
, LAST_LOAD_DT_KEY_NO
, LAST_UPDT_PROC_KEY_NO
, LAST_LOAD_PROC_KEY_NO
, LOS_GRP_KEY_NO
, contb_distb_flg)
SELECT /*+ PARALLEL (IMC 8)*/
CAST(TO_CHAR(ADD_MONTHS(SYSDATE,-1),'YYYYMM') as NUMERIC (10,0))AS SNAP_MO_YR_KEY_NO
, IMC.IMC_KEY_NO
, IMC.IMC_AFF_KEY_NO
, IMC.IMC_CNTRY_KEY_NO
, IMC.IMC_NAME
, NVL(CNTAC.PRM_STATE,CNTAC.PRM_PROV)
, CNTAC.PRM_POST_CODE
, IMC.IMC_TYPE_CD
, CASE WHEN trim(DERV.ENGAGE_FLG) = 'Y' THEN 1 else 0 END
, DERV.IMC_CURR_SEG_KEY_NO
, IMC.APPL_DT_KEY_NO
, DERV.RENEW_DT_KEY_NO
, IMC.IMC_DLETE_DT_KEY_NO
, IMC.SPON_IMC_KEY_NO
, IMC.IMC_CLASS_CD
, DERV.IMC_HIGH_AWD_KEY_NO
, DERV.IMC_ACHV_AWD_KEY_NO
, DERV.IMC_CURR_QUAL_AWD_KEY_NO
, IMC.ISPON_FLG
, IMC.ISPON_AFF_ID
, CNTAC.PRM_LANG_CD
, IMC.ISPON_IMC_KEY_NO
, DERV.EXPIRE_DT_KEY_NO
, DERV.FRONTLN_DISTB_CNT --FRONTLINE_CNT
, CAST(case
when (TO_DATE(TO_CHAR(last_day(ADD_MONTHS(SYSDATE,-1)),'YYYYMMDD'),'YYYYMMDD') - TO_DATE (IMC.APPL_DT_KEY_NO,'YYYYMMDD')) + 1 < 1 then 1
else (TO_DATE(TO_CHAR(last_day(ADD_MONTHS(SYSDATE,-1)),'YYYYMMDD'),'YYYYMMDD') - TO_DATE (IMC.APPL_DT_KEY_NO,'YYYYMMDD')) + 1
end AS NUMERIC (10,0)) as LOM_DY_NO
, IMC.IMC_LOA_KEY_NO
, IMC.GLOBL_IMC_TYPE_KEY_NO
, CNTAC.POSTL_CD_KEY_NO
, IMC.STATUS_KEY_NO
, DERV.LAST_ORD_OIMC_DT_KEY_NO
, DERV.LAST_ORD_VIMC_DT_KEY_NO
, DERV.LAST_SPON_DT_KEY_NO
, CAST(TO_CHAR(SYSDATE, 'YYYYMMDD')as numeric(10,0)) AS LAST_UPDT_DT_KEY_NO
, CAST(TO_CHAR(SYSDATE, 'YYYYMMDD')as numeric(10,0)) as LAST_LOAD_DT_KEY_NO
, CAST(-1 AS NUMERIC(10,0)) as LAST_UPDT_PROC_KEY_NO
, CAST(-1 AS NUMERIC(10,0)) as LAST_LOAD_PROC_KEY_NO
, IMC.LOS_GRP_KEY_NO
, CASE WHEN DT.DT_KEY_NO IS NULL THEN 'N'
ELSE 'Y' END AS CONTB_DISTB_FLG
FROM DWSGDW01.DWT00740_IMC_DIM IMC, DWV00002_BUS_STAT_DIM BUS, DWT00410_IMC_DERV_DIM DERV, DWSGDW01.DWT00750_IMC_CNTAC_DIM CNTAC
, (SELECT * FROM DWSGDW01.MV00002_DT_DIM WHERE MO_YR_KEY_NO = CAST ( TO_CHAR(ADD_MONTHS(SYSDATE, -1), 'YYYYMM') as NUMERIC (10,0))) DT
where DERV.IMC_KEY_NO = IMC.IMC_KEY_NO and BUS.STATUS_KEY_NO = IMC.STATUS_KEY_NO AND CNTAC.IMC_KEY_NO = IMC.IMC_KEY_NO
and ((APPL_DT_KEY_NO < to_char(last_day(SYSDATE),'YYYYMMDD')
AND (IMC_DLETE_DT_KEY_NO = 19000101
OR TO_CHAR(ADD_MONTHS(TO_DATE(IMC_DLETE_DT_KEY_NO, 'YYYYMMDD'),12),'YYYY-MM-DD') > to_char(last_day(SYSDATE),'YYYY-MM-DD') ))
OR BUS.GLOBL_BUS_STAT_CD ='ACTIVE');


Error Report

SQL Error: ORA-12838: cannot read/modify an object after modifying it in parallel
12838. 00000 - "cannot read/modify an object after modifying it in parallel"
*Cause: Within the same transaction, an attempt was made to add read or
modification statements on a table after it had been modified in parallel
or with direct load. This is not permitted.
*Action: Rewrite the transaction, or break it up into two transactions
one containing the initial modification and the second containing the
parallel modification operation.

what happens if/when the APPEND hint is removed/eliminated?

I did so

INSERT INTO DWSGDW01.DWT00050_IMC_CCYYMM_FACT (
SNAP_MO_YR_KEY_NO
, IMC_KEY_NO
, IMC_AFF_KEY_NO
, IMC_CNTRY_KEY_NO
, IMC_DERIVED_NM
, IMC_ST_PROV_CD
, IMC_POSTL_CD
, IMC_TYPE_CD
, ENGAGE_FLG
, IMC_CURR_SEG_KEY_NO
, IMC_APPL_DT_KEY_NO
, LAST_RENEW_DT_KEY_NO
, IMC_DLETE_DT_KEY_NO
, SPON_IMC_KEY_NO
, IMC_CLASS_CD
, IMC_HIGH_AWD_KEY_NO
, IMC_ACHV_AWD_KEY_NO
, IMC_CURR_QUAL_AWD_KEY_NO
, IMC_ISPON_FLG
, IMC_ISPON_AFF_ID
, IMC_LANG_CD
, IMC_ISPON_IMC_KEY_NO
, IMC_EXPIRE_DT_KEY_NO
, FRONTLINE_CNT
, LOM_DY_NO
, LOA_KEY_NO
, GLOBL_IMC_TYPE_KEY_NO
, POSTL_CD_KEY_NO
, STATUS_KEY_NO
, LAST_ORD_OIMC_DT_KEY_NO
, LAST_ORD_VIMC_DT_KEY_NO
, LAST_SPON_DT_KEY_NO
, LAST_UPDT_DT_KEY_NO
, LAST_LOAD_DT_KEY_NO
, LAST_UPDT_PROC_KEY_NO
, LAST_LOAD_PROC_KEY_NO
, LOS_GRP_KEY_NO
, CONTB_DISTB_FLG)
SELECT /*+ PARALLEL (IMC 8)*/
CAST(TO_CHAR(ADD_MONTHS(SYSDATE,-1),'YYYYMM') as NUMERIC (10,0))AS SNAP_MO_YR_KEY_NO
, IMC.IMC_KEY_NO
, IMC.IMC_AFF_KEY_NO
, IMC.IMC_CNTRY_KEY_NO
, IMC.IMC_NAME
, NVL(CNTAC.PRM_STATE,CNTAC.PRM_PROV)
, CNTAC.PRM_POST_CODE
, IMC.IMC_TYPE_CD
, CASE WHEN trim(DERV.ENGAGE_FLG) = 'Y' THEN 1 else 0 END
, DERV.IMC_CURR_SEG_KEY_NO
, IMC.APPL_DT_KEY_NO
, DERV.RENEW_DT_KEY_NO
, IMC.IMC_DLETE_DT_KEY_NO
, IMC.SPON_IMC_KEY_NO
, IMC.IMC_CLASS_CD
, DERV.IMC_HIGH_AWD_KEY_NO
, DERV.IMC_ACHV_AWD_KEY_NO
, DERV.IMC_CURR_QUAL_AWD_KEY_NO
, IMC.ISPON_FLG
, IMC.ISPON_AFF_ID
, CNTAC.PRM_LANG_CD
, IMC.ISPON_IMC_KEY_NO
, DERV.EXPIRE_DT_KEY_NO
, DERV.FRONTLN_DISTB_CNT --FRONTLINE_CNT
, CAST(case
when (TO_DATE(TO_CHAR(last_day(ADD_MONTHS(SYSDATE,-1)),'YYYYMMDD'),'YYYYMMDD') - TO_DATE (IMC.APPL_DT_KEY_NO,'YYYYMMDD')) + 1 < 1 then 1
else (TO_DATE(TO_CHAR(last_day(ADD_MONTHS(SYSDATE,-1)),'YYYYMMDD'),'YYYYMMDD') - TO_DATE (IMC.APPL_DT_KEY_NO,'YYYYMMDD')) + 1
end AS NUMERIC (10,0)) as LOM_DY_NO
, IMC.IMC_LOA_KEY_NO
, IMC.GLOBL_IMC_TYPE_KEY_NO
, CNTAC.POSTL_CD_KEY_NO
, IMC.STATUS_KEY_NO
, DERV.LAST_ORD_OIMC_DT_KEY_NO
, DERV.LAST_ORD_VIMC_DT_KEY_NO
, DERV.LAST_SPON_DT_KEY_NO
, CAST(TO_CHAR(SYSDATE, 'YYYYMMDD')as numeric(10,0)) AS LAST_UPDT_DT_KEY_NO
, CAST(TO_CHAR(SYSDATE, 'YYYYMMDD')as numeric(10,0)) as LAST_LOAD_DT_KEY_NO
, CAST(-1 AS NUMERIC(10,0)) as LAST_UPDT_PROC_KEY_NO
, CAST(-1 AS NUMERIC(10,0)) as LAST_LOAD_PROC_KEY_NO
, IMC.LOS_GRP_KEY_NO
, CASE WHEN DT.DT_KEY_NO IS NULL THEN 'N'
ELSE 'Y' END AS CONTB_DISTB_FLG
FROM DWSGDW01.DWT00740_IMC_DIM IMC, DWV00002_BUS_STAT_DIM BUS, DWT00410_IMC_DERV_DIM DERV, DWSGDW01.DWT00750_IMC_CNTAC_DIM CNTAC
, (SELECT * FROM DWSGDW01.MV00002_DT_DIM WHERE MO_YR_KEY_NO = CAST ( TO_CHAR(ADD_MONTHS(SYSDATE, -1), 'YYYYMM') as NUMERIC (10,0))) DT
where DERV.IMC_KEY_NO = IMC.IMC_KEY_NO and BUS.STATUS_KEY_NO = IMC.STATUS_KEY_NO AND CNTAC.IMC_KEY_NO = IMC.IMC_KEY_NO
and ((APPL_DT_KEY_NO < to_char(last_day(SYSDATE),'YYYYMMDD')
AND (IMC_DLETE_DT_KEY_NO = 19000101
OR TO_CHAR(ADD_MONTHS(TO_DATE(IMC_DLETE_DT_KEY_NO, 'YYYYMMDD'),12),'YYYY-MM-DD') > to_char(last_day(SYSDATE),'YYYY-MM-DD') ))
OR BUS.GLOBL_BUS_STAT_CD ='ACTIVE');

Error Report

SQL Error: ORA-00001: unique constraint (DWSGDW01.DWI00050CC_SNAP_MO_YR_K_IMC_K) violated
00001. 00000 - "unique constraint (%s.%s) violated"
*Cause: An UPDATE or INSERT statement attempted to insert a duplicate key.
For Trusted Oracle configured in DBMS MAC mode, you may see
this message if a duplicate entry exists at a different level.
*Action: Either remove the unique restriction or do not insert the key.

Stored Procedure Error

It is de'javu all over again.

We have met the enemy, & they is us.

UNIQUE constraint does not allow duplicate key values.