有很多种方法可以用来找出哪些sql语句需要优化，但是很久以来，最简单的方法都是分析保存在V$sql视图中的缓存的sql信息。通过V$sql视图，可以确定具有高消耗时间、CUP和IO读取的sql语句。

1.查看总消耗时间最多的前10条sql语句
select *
from (select v.sql_id,
v.child_number,
v.sql_text,
last_load_time,
v.PARSING_USER_ID,
ROUND(v.ELAPSED_TIME / 1000000 / (CASE
WHEN (EXECUTIONS = 0 OR NVL(EXECUTIONS,1 ) = 1) THEN
1
ELSE
EXECUTIONS
END),
2) "执行时间'S'",
v.sql_FULLTEXT,
v.cpu_time,
v.disk_reads,
rank() over(order by v.elapsed_time desc) elapsed_rank
from v$sql v ) a
where elapsed_rank <= 100 and last_load_time > to_char(sysdate - 1/24,'YYYY-MM-DD/HH:MI:SS') order by "执行时间'S'" desc

查询最近一小时内最慢的sql:

select executions,cpu_time/1e6 as cpu_sec,elapsed_time/1e6 as elapsed_sec,round(elapsed_time/sqrt(executions)) as important,v.*
from v$sql v
where executions > 10 and last_load_time > to_char(sysdate - 1/24,'YYYY-MM-DD/HH:MI:SS')
order by important desc

2.查看cpu消耗时间最多的前10条sql语句
select *
from (select v.sql_id,
v.elapsed_time,
rank() over(order by v.cpu_time desc) elapsed_rank
from v$sql v) a
where elapsed_rank <= 10;

3.查看消耗磁盘读取最多的前10条sql语句
select *
from (select v.sql_id,
rank() over(order by v.disk_reads desc) elapsed_rank
from v$sql v) a
where elapsed_rank <= 10;

一、查询执行最慢的sql

二、查询次数最多的 sql