Payroll: Update Value from one Def ID to another

Preview

select H.DEF_VALUE,
(select DEF_VALUE from prtempdefhst H2 where def_id='FEDGRS' AND H2.SESSION_NO=H.SESSION_NO
    AND H2.TRANS_NO=H.TRANS_NO),H.*
 from prtempdefhst H where def_id='LA_GROSS' 
AND H.DEF_VALUE<>(select DEF_VALUE from prtempdefhst H2 where def_id='FEDGRS' AND H2.SESSION_NO=H.SESSION_NO
    AND H2.TRANS_NO=H.TRANS_NO)

Update

update  prtempdefhst H  set
H.DEF_VALUE=(select DEF_VALUE from prtempdefhst H2 where def_id='FEDGRS' AND H2.SESSION_NO=H.SESSION_NO
    AND H2.TRANS_NO=H.TRANS_NO) 
where def_id='LA_GROSS' 
AND H.DEF_VALUE<>(select DEF_VALUE from prtempdefhst H2 where def_id='FEDGRS' AND H2.SESSION_NO=H.SESSION_NO
    AND H2.TRANS_NO=H.TRANS_NO)