title: ORA-01407:cannot update to null
body: <p>My sql query for updating column "p1_high_edu_ctry" is:-</p>
  
  <pre><code> update ps_personal_data J
   set (J.p1_high_edu_ctry) = (SELECT P.p1_high_edu_ctry FROM PS_PERS_DATA_EFFDT P 
   WHERE P.EFFDT=(SELECT MAX(K.EFFDT) FROM PS_PERS_DATA_EFFDT K
   WHERE K.EFFDT&lt;=SYSDATE
   AND   J.EMPLID IN(SELECT H.EMPLID FROM PS_AUDIT_PER_EFFDT H 
   where h.AUDIT_OPRID='CHGH00000063232')))
   where exists(select 1 from PS_AUDIT_PER_EFFDT q where q.emplid=j.emplid) ;
  </code></pre>
  
  <p>but i m getting an error msg while updating:-</p>
  
  <pre><code>ERROR at line 2:
  ORA-01407: cannot update ("SYSADM"."PS_PERSONAL_DATA"."P1_HIGH_EDU_CTRY") to NULL
  </code></pre>
  
  <p>Any suggestions please,why its not working even if i am handling it with where exists???</p>