数据库缓冲区命中率

select 1 - ((select to_number(value)
               from v$sysstat t
              where t.name = 'physical reads') -
       (select to_number(value)
               from v$sysstat t
              where t.name = 'physical reads direct') -
       (select to_number(value)
               from v$sysstat t
              where t.name = 'physical reads direct (lob)')) /
       (select to_number(value)
              from v$sysstat t
             where t.name = 'session logical reads')
  from dual;