性能优化之查看bad sql语句

      在oracle性能优化过程中，查出bad sql(即sql语句有问题)并根据查询结果来优化语句达到优化性能的目的的手段是很普遍的，下面是一些查询bad sql的sql语句，与大家分享！
-- 逻辑读多的SQL
select * from (select buffer_gets, sql_text
from v$sqlarea
where buffer_gets > 500000
order by buffer_gets desc) where rownum<=30;

-- 执行次数多的SQL   
  select sql_text,executions from
  (select sql_text,executions from v$sqlarea order by executions desc)
   where rownum<81;

-- 读硬盘多的SQL 
  select sql_text,disk_reads from
  (select sql_text,disk_reads from v$sqlarea order by disk_reads desc)
   where rownum<21;    

-- 排序多的SQL   
  select sql_text,sorts from
   (select sql_text,sorts from v$sqlarea order by sorts desc)
    where rownum<21;           
 
--分析的次数太多，执行的次数太少，要用绑变量的方法来写sql
set pagesize 600;
set linesize 120;
select substr(sql_text,1,80) "sql", count(*), sum(executions) "totexecs"
   from v$sqlarea
   where executions < 5
   group by substr(sql_text,1,80)
   having count(*) > 30
   order by 2;