substr()

              
update ncdata.er_bxzb c
   set c.zyx4 = 0
 where c.djbh in (select a.djbh
                    from ncdata.er_bxzb a
                    left join ncdata.org_orgs b
                      on a.pk_org = b.pk_org
                   where a.djlxbm = '2647'
                     and substr(a.zyx4, 0, 1) = '-'
                   order by a.djrq);