SQL查询中断号

with tmp as(
        select rownum r from dual connect by level (select max(CAST(VOLUMENUM as integer)) from ARCHIVEITEM t where TO_CHAR(t.ARCHIVEDATE,'yyyy') = TO_CHAR(SYSDATE,'yyyy') and CLASSNUM=#{classnum})
        )
        select min(r)  from tmp a  where not exists (select CAST(VOLUMENUM as integer) from ARCHIVEITEM where CAST(VOLUMENUM as integer)=a.r and TO_CHAR(ARCHIVEDATE,'yyyy') = TO_CHAR(SYSDATE,'yyyy') and CLASSNUM=#{classnum} )