V$SQL*表用于查看Shared SQL Area中SQL情况
V$SQLTEXT
V$SQLTEXT用途很简单，就是用来查看完整的SQL语句，V$SQL和V$SQLAREA只能显示1000 bytes，且特殊字符用空格替代。
This view contains the text of SQL statements belonging to shared SQL cursors in the SGA.
Column Datatype Description
ADDRESS RAW(4 | 8) Used with HASH_VALUE to uniquely identify a cached cursor
HASH_VALUE NUMBER Used with ADDRESS to uniquely identify a cached cursor
SQL_ID VARCHAR2(13) SQL identifier of a cached cursor
COMMAND_TYPE NUMBER Code for the type of SQL statement (SELECT, INSERT, and so on)
PIECE NUMBER Number used to order the pieces of SQL text
SQL_TEXT VARCHAR2(64) A column containing one piece of the SQL text
Example:
SELECT 'PTIAN' FROM DUAL;
SELECT * FROM V$SQLTEXT WHERE SQL_TEXT LIKE '%PTIAN%';
Output:
ADDRESS HASH_VALUE SQL_ID COMMAND_TYPE PIECE SQL_TEXT
000000008774FF80 2034677615 57zcfn1wnddvg 3 0 select * from v$sqltext where SQL_TEXT LIKE '%PTIAN%'
000000008760AC20 2521097521 ak2vyjub49t9j 3 0 SELECT 'PTIAN' FROM DUAL
V$SQL & V$SQLAREA
V$SQL , V$SQLAREA很类似，看下Tom的解释：
v$sql the details -- if you have multiple copies of the query:
"select * from T"
in your shared pool, v$sql will have a row per query. This can happen if user U1 and user U2 both have a table T and both issue "select * from T". Those are entirely different queries with different plans and so on. v$sql will have 2 rows.
v$sqlarea is a aggregate of v$sql. It selects out DISTINCT sql. "select * from T" will appear there.
v$sqltext is simply a way to see the entire query. the v$sql and v$sqlarea views only show the first 1000 bytes. newlines and other control characters are replace with whitespace.
v$sqltext_with_newlines is v$sqltext without the whitespace replacment.
v$sql ---------- 存储的是具体的SQL 和执行计划相关信息，实际上，v$sqlarea 可以看做 v$sql 根据 sqltext 等 做了 group by 之后的信息
v$sqlarea --------- 存储的SQL 和一些相关的信息，比如累计的执行次数，逻辑读，物理读等统计信息
而v$SQLAREA 忽略了 执行计划 等差异，只是在形式上sql文本看起来一样！相当于做了个聚合，是多个不同执行计划的sql的聚合和累计信息
(refer:http://www.itpub.net/forum.php?mod=viewthread&tid=181450&page=1)
v$sql与v$sqlarea的源都是一个：X$KGLCURSOR
实际调优中建议使用v$sql,相对来说比v$sqlarea快，而且还不会产生share pool latch的争用
(refer:http://www.itpub.net/thread-522899-1-1.html)
共同点：
1）都存储了sql内容
2) 记录的都是位于内存中的sql内容
3) 因为是内存，所以都不保留历史记录
不同点：
1)存储的为止不都是相同。其中v$sql和v$sqlarea存储的sql都是位于shared sql area中的sql,而v$sqltext是位于sga中的sql。但文档没有明确说明这里的sga是否还包含了psa(私有sql区域－－共享服务器模式下）。
2)存储sql的方式也不同，v$sql和v$sqlarea都是用一行来存储sql全文，而v$sqltext用一行存储sql的一行。
3)v$sql不存储包含group by 的sql语句。通常这个视图，在每个查询执行完成后更新，但对于执行很久的sql,它是每5秒更新一次，这点对于查看sql执行状态是有意义的。
4)存储的明细不同－－这是最基本的。
最后顺便提一下，v$sqltext_with_newline和v$sqltext是一样，不同的是前者并把换行符和tab替换为空格 ，这样更容易阅读。V$SQLSTATS和V$SQL,v$sqlarea一样都有提供CPU的统计数据.
(Refer:http://lzfhope.blog.163.com/blog/static/63639922008101955913105/)
一些用法:
1.Find top 5 queries with most disk_reads
SELECT SESION.SID,
SESION.USERNAME,
OPTIMIZER_MODE,
HASH_VALUE,
ADDRESS,
CPU_TIME,
ELAPSED_TIME,
DISK_READS,
DIRECT_WRITES,
SQL_TEXT
FROM V$SQLAREA SQLAREA, V$SESSION SESION
WHERE SESION.SQL_HASH_VALUE = SQLAREA.HASH_VALUE
AND SESION.SQL_ADDRESS = SQLAREA.ADDRESS
AND SESION.USERNAME IS NOT NULL
AND ROWNUM < 6
ORDER BY DISK_READS DESC,ELAPSED_TIME DESC;
2.See what SQL users are running on the system
select a.sid, a.serial#, b.sql_text
from v$session a, v$sqlarea b
where a.sql_address=b.address
and a.username='GRUMPY';
SID SERIAL# SQL_TEXT
---------- ---------- ----------------------------------------------
122 61521 select count(*) from gen_person where gen_person_id=95000
