1.曾经不小心把开发库的数据库表全部删除，当时吓的要死。结果找到下面的语句恢复到了1个小时之前的数据！很简单。
注意使用管理员登录系统：
select * from 表名 as of timestamp sysdate-1/12 //查询两个小时前的某表数据！既然两小时以前的数据都得到了，继续怎么做，知道了吧。。
如果drop了表，怎么办？？见下面：
drop table 表名;
数据库误删除表之后恢复:（ 绝对ok，我就做过这样的事情，汗 ）不过要记得删除了哪些表名。
flashback table 表名 to before drop;
2.查询得到当前数据库中锁，以及解锁：
查锁
SELECT /*+ rule */ s.username,
decode(l.type,'TM','TABLE LOCK',
'TX','ROW LOCK',
NULL) LOCK_LEVEL,
o.owner,o.object_name,o.object_type,
s.sid,s.serial#,s.terminal,s.machine,s.program,s.osuser
FROM v$session s,v$lock l,dba_objects o
WHERE l.sid = s.sid
AND l.id1 = o.object_id(+)
AND s.username is NOT NULL;
解锁
alter system kill session 'sid,serial';
如果解不了。直接倒os下kill进程kill －9 spid
SELECT /*+ rule */ s.username,
decode(l.type,'TM','TABLE LOCK',
'TX','ROW LOCK',
NULL) LOCK_LEVEL,
o.owner,o.object_name,o.object_type,
s.sid,s.serial#,s.terminal,s.machine,s.program,s.osuser
FROM v$session s,v$lock l,dba_objects o
WHERE l.sid = s.sid
AND l.id1 = o.object_id(+)
AND s.username is NOT NULL;
解锁
alter system kill session 'sid,serial';
如果解不了。直接倒os下kill进程kill －9 spid
5.查看当前数据库中正在执行的语句，然后可以继续做很多很多事情，例如查询执行计划等等
Sql代码 
- (1).查看相关进程在数据库中的会话
- Select a.sid,a.serial#,a.program, a.status ,
- substr(a.machine,1,20), a.terminal,b.spid
- from v$session a, v$process b
- where a.paddr=b.addr
- and b.spid = &spid;
- (2).查看数据库中被锁住的对象和相关会话
- select a.sid,a.serial#,a.username,a.program,
- c.owner, c.object_name
- from v$session a, v$locked_object b, all_objects c
- where a.sid=b.session_id and
- c.object_id = b.object_id;
- (3).查看相关会话正在执行的SQL
- select sql_text from v$sqlarea where address =
- ( select sql_address from v$session where sid = &sid );
6.查询表的结构：表名大写！！
select t.COLUMN_NAME,
t.DATA_TYPE,
nvl(t.DATA_PRECISION, t.DATA_LENGTH),
nvl(T.DATA_SCALE, 0),
c.comments
from all_tab_columns t, user_col_comments c
whEre t.TABLE_NAME = c.table_name
and t.COLUMN_NAME = c.column_name
and t.TABLE_NAME = UPPER('OM_EMPLOYEE_T')
order by t.COLUMN_ID
t.DATA_TYPE,
nvl(t.DATA_PRECISION, t.DATA_LENGTH),
nvl(T.DATA_SCALE, 0),
c.comments
from all_tab_columns t, user_col_comments c
whEre t.TABLE_NAME = c.table_name
and t.COLUMN_NAME = c.column_name
and t.TABLE_NAME = UPPER('OM_EMPLOYEE_T')
order by t.COLUMN_ID
7.行列互换：
Sql代码
- 建立一个例子表：
- CREATE TABLE t_col_row(
- ID INT,
- c1 VARCHAR2(10),
- c2 VARCHAR2(10),
- c3 VARCHAR2(10));
- INSERT INTO t_col_row VALUES (1, 'v11', 'v21', 'v31');
- INSERT INTO t_col_row VALUES (2, 'v12', 'v22', NULL);
- INSERT INTO t_col_row VALUES (3, 'v13', NULL, 'v33');
- INSERT INTO t_col_row VALUES (4, NULL, 'v24', 'v34');
- INSERT INTO t_col_row VALUES (5, 'v15', NULL, NULL);
- INSERT INTO t_col_row VALUES (6, NULL, NULL, 'v35');
- INSERT INTO t_col_row VALUES (7, NULL, NULL, NULL);
- COMMIT;
- 下面的是列转行:创建了一个视图
- CREATE view v_row_col AS
- SELECT id, 'c1' cn, c1 cv
- FROM t_col_row
- UNION ALL
- SELECT id, 'c2' cn, c2 cv
- FROM t_col_row
- UNION ALL
- SELECT id, 'c3' cn, c3 cv FROM t_col_row;
- 下面是创建了没有空值的一个竖表:
- CREATE view v_row_col_notnull AS
- SELECT id, 'c1' cn, c1 cv
- FROM t_col_row
- where c1 is not null
- UNION ALL
- SELECT id, 'c2' cn, c2 cv
- FROM t_col_row
- where c2 is not null
- UNION ALL
- SELECT id, 'c3' cn, c3 cv
- FROM t_col_row
- where c3 is not null;
8.下面可能是dba经常使用的oracle视图吧。呵呵
Sql代码
- 1.示例：已知hash_value:3111103299，查询sql语句：
- select * from v$sqltext
- where hashvalue='3111103299'
- order by piece
- 2.查看消耗资源最多的SQL：
- SELECT hash_value, executions, buffer_gets, disk_reads, parse_calls
- FROM V$SQLAREA
- WHERE buffer_gets > 10000000OR disk_reads > 1000000
- ORDERBY buffer_gets + 100 * disk_reads DESC;
- 3.查看某条SQL语句的资源消耗：
- SELECT hash_value, buffer_gets, disk_reads, executions, parse_calls
- FROM V$SQLAREA
- WHERE hash_Value = 228801498AND address = hextoraw('CBD8E4B0');
- 4.查询sql语句的动态执行计划:
- 首先使用下面的语句找到语句的在执行计划中的address和hash_code
- SELECT sql_text, address, hash_value FROM v$sql t
- where (sql_text like '%FUNCTION_T(表名大写!)%')
- 然后:
- SELECT operation, options, object_name, cost FROM v$sql_plan
- WHERE address = 'C00000016BD6D248' AND hash_value = 664376056;
- 5.查询oracle的版本:
- select * from v$version;
- 6.查询数据库的一些参数:
- select * from v$parameter
- 7.查找你的session信息
- SELECT SID, OSUSER, USERNAME, MACHINE, PROCESS
- FROM V$SESSION WHERE audsid = userenv('SESSIONID');
- 8.当machine已知的情况下查找session
- SELECT SID, OSUSER, USERNAME, MACHINE, TERMINAL
- FROM V$SESSION
- WHERE terminal = 'pts/tl' AND machine = 'rgmdbs1';
- 9.查找当前被某个指定session正在运行的sql语句。假设sessionID为100
- select b.sql_text
- from v$session a,v$sqlarea b
- where a.sql_hashvalue=b.hash_value and a.sid=100
9.树形结构connect by 排序：
Sql代码
- 查询树形的数据结构，同时对一层里面的数据进行排序
- SELECT last_name, employee_id, manager_id, LEVEL
- FROM employees
- START WITH employee_id = 100
- CONNECT BY PRIOR employee_id = manager_id
- <span style="background-color: #ff0000;"> ORDER SIBLINGS BY last_name;</span>
- 下面是查询结果
- LAST_NAME EMPLOYEE_ID MANAGER_ID LEVEL
- ------------------------- ----------- ---------- ----------
- King 100 1
- Cambrault 148 100 2
- Bates 172 148 3
- Bloom 169 148 3
- Fox 170 148 3
- Kumar 173 148 3
- Ozer 168 148 3
- Smith 171 148 3
- De Haan 102 100 2
- Hunold 103 102 3
- Austin 105 103 4
- Ernst 104 103 4
- Lorentz 107 103 4
- Pataballa 106 103 4
- Errazuriz 147 100 2
- Ande 166 147 3
- Banda 167 147 3
