Oracle sql语句执行顺序
- - 数据库 - ITeye博客sql语法的分析是从右到左. 一、sql语句的执行步骤:. 1)语法分析,分析语句的语法是否符合规范,衡量语句中各表达式的意义. 2)语义分析,检查语句中涉及的所有数据库对象是否存在,且用户有相应的权限. 3)视图转换,将涉及视图的查询语句转换为相应的对基表查询语句. 4)表达式转换, 将复杂的 SQL 表达式转换为较简单的等效连接表达式.
--查看Oracle数据库字符集:
select userenv('language') from dual;
---正在执行的
select a.username, a.sid, b.SQL_TEXT, b.SQL_FULLTEXT
from v$session a, v$sqlarea b
where a.sql_address = b.address;
---执行过的 (此方法好处可以查看某一时间段执行过的sql,并且 SQL_FULLTEXT 包含了完整的 sql 语句)
select b.SQL_TEXT, b.FIRST_LOAD_TIME, b.SQL_FULLTEXT
from v$sqlarea b
where b.FIRST_LOAD_TIME between '2009-10-15/09:24:47' and
'2009-10-15/09:24:47'
order by b.FIRST_LOAD_TIME;
--其他
select OSUSER,
PROGRAM,
USERNAME,
SCHEMANAME,
B.Cpu_Time,
STATUS,
B.SQL_TEXT
from V$SESSION A
LEFT JOIN V$SQL B
ON A.SQL_ADDRESS = B.ADDRESS
AND A.SQL_HASH_VALUE = B.HASH_VALUE
order by b.cpu_time desc;
select address, sql_text, piece
from v$session, v$sqltext
where address = sql_address
-- and machine = < you machine name >
order by address, piece;
-- 查找前十条性能差的sql.
SELECT *
FROM (select PARSING_USER_ID,
EXECUTIONS,
SORTS,
COMMAND_TYPE,
DISK_READS,
sql_text
FROM v$sqlarea
order BY disk_reads DESC)
where ROWNUM < 10;
--查看占io较大的正在运行的session
SELECT se.sid,
se.serial#,
pr.SPID,
se.username,
se.status,
se.terminal,
se.program,
se.MODULE,
se.sql_address,
st.event,
st. p1text,
si.physical_reads,
si.block_changes
FROM v$session se, v$session_wait st, v$sess_io si, v$process pr
WHERE st.sid = se.sid
AND st. sid = si.sid
AND se.PADDR = pr.ADDR
AND se.sid > 6
AND st. wait_time = 0
AND st.event NOT LIKE '%SQL%'
ORDER BY physical_reads DESC;