The following select query is to join 2 tables to give me the list of employees who are terminated: select a.YEAN8, a.YEHMCU, b.YAALPH, b.YADT, b.YAPTDT , a.YEPSDT, a.YEPTDT from CRPDTA.F060118 a, CRPDTA.F060116 b where a.YEAN8 = b.YAAN8 and a.YEHMCU = 229 and b.YAPAST = 'T'; Goal is to populate last column 'YEPTDT' to be the same as 'YADT. Wrote the following update query: update CRPDTA.F060118 set YEPTDT = (select b.YADT from CRPDTA.F060116 b where CRPDTA.F060118.YEAN8 = b.YAAN8 and b.YAHMCU = 229 and b.YAPAST = 'T'); However, got the following error: Error report - SQL Error: ORA-01407: cannot update ("CRPDTA"."F060118"."YEPTDT") to NULL 01407. 00000 - "cannot update (%s) to NULL" Now I know that column 'YEPTDT' does not allow NULL. However, as I verified in my first select statement that there are values in 'YADT' and no NULL. Any idea how to get around it?