分析性能差的sql

--EXECUTIONS 所有子游标的执行这条语句次数 
--DISK_READS 所有子游标运行这条语句导致的读磁盘次数 
--BUFFER_GETS 所有子游标运行这条语句导致的读内存次数 
--Hit_radio 命中率 
--Reads_per_run 每次执行读写磁盘数 

SELECT EXECUTIONS,
       DISK_READS,
       BUFFER_GETS,
       ROUND((BUFFER_GETS - DISK_READS) / BUFFER_GETS, 2) Hit_radio,
       ROUND(DISK_READS / EXECUTIONS, 2) Reads_per_run,
       SQL_TEXT
  FROM v$SQLAREA
 WHERE EXECUTIONS > 0
   AND BUFFER_GETS > 0
   AND (BUFFER_GETS - DISK_READS) / BUFFER_GETS < 0.8
 ORDER BY 4 DESC;