inner join 和 left join

select
  v.usercode,
  t.menucode,
  t.menuname,
  t.linkpage,
  t.menulevel,
  t.ordernum,
  t.parentcode,
  t.icoindex,
  t.selicoindex,t.ismenu,t.pageflag,t.isshow,t.issysmenu,t.isvalid,t.sourcelevel
from DFO.SYS_MENUINFO t
inner join (
     select usercode,menucode from (
            select
               a.usercode,
               b.menucode
            from sys_userrole a
            inner join DFO.Sys_Rolepower b on a.rolecode = b.rolecode
            left join DFO.sys_roleinfo c on a.rolecode = c.rolecode
            where usercode = 'yh00000007' and nvl(c.isvalid,'0')='1'
      )
      group by usercode,menucode
    ) v
on t.menucode = v.menucode 
WHERE 1=1
AND ISSHOW ='1'
AND ISVALID ='1'
AND menulevel ='1'
ORDER BY menucode,ordernum