oracle的内存结构
数据库的内存结构：
Memory structures are allocated to the Oracle instance when the instance is started.
The two major memory structures are known as the System Global Area(Also called the shared
Global Area)and the Program Global Area(also called the Private Global Area or the Process
Global Area)
SGA:
The System Global Area(SGA) is a shared memory area.All users of the database share the
information maintained in this area.The SGA and the backgroud processes constitute an Oracle instance.Oracle allocates memory for the SGA when an Oracle instance is started and de-allocates it when the istance is shut down.The information stored in the SGA is divided into multiple memory structures that are allocated fixed space when the instance started.
DATABASE Buffer Cache:
The database buffer cache is the area of memory that caches the database area,holding blocks
from the data files that have been read recently.The DB buffer cache is shared among all the users connected to the database.
There are three type of buffers.
Dirty buffers:Dirty buffers are the buffer blocks that need to be written to the data files.
The data in these buffers has changed and has not yet been written ti the disk.
Free buffers :Free buffers do not contain any data or are free to be overwritten.When Oracle reads data from disk,free buffers are used to hold this area.
Pinned buffers :Pinned buffers are the ones that are currently being accessed or explicityly retained for futer use.(for example,the KEEP buffer)
Oracle maintains two lists to manage the buffer cache,The write list(dirty buffer list) has the buffers that are modified and need to be written to the disk(the dirty buffers).
The least recently used(LRU) list contains fr
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oracle表空间操作详解
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3作者： 来源： 更新日期：2006-01-04
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7建立表空间
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9CREATE TABLESPACE data01
10DATAFILE '/ora ......
1、查找表的所有索引（包括索引名，类型，构成列）：
select t.*,i.index_type from user_ind_columns t,user_indexes i where t.index_name = i.index_name and t.table_name = i.table_name and t.table_name = 要查询的表
2、查找表的主键（包括名称，构成列）：
select cu.* from user_cons_columns cu, user_constr ......
select lower( column_name) ||','||'--'||comments
from user_col_comments c
where c.table_name = upper('acc_fundcap')
SELECT * from USER_TAB_COMMENTS WHERE TABLE_NAME='T_META';
INSERT INTO 表名(字段名1, 字段名2) SELECT 字段名1, 字段名2 from 另外的表名; ......
先看下面的例子:oracle中两个系统表.emp,dept.
example:
1:not exists(not in)
not exists:
这条语句返回select * from scott.dept d where e.deptno=d.deptno and d.deptno=10条件满足的结果集.也就是说,
返回的结果集中不存在d.deptno=10结果集的记录,即emp表中没有dept表中d.deptno=10的记录.
SQL& ......
