oracle 优化之 找出低效率sql 语句

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;