ORACLE HWM 和 low HWM
今天在学习的过程中看到了LOW HWM，印象中以前在什么地方看到过可是死活想不起来，去百度了半天都没找到相关的信息。无奈之下还是GOOGLE了一下，找到一篇asktom上的帖子。记录在这里，顺便和大家分享一下。
High-water Mark
This is a term used with table segments stored in the database. If you envision a table, for example, as a 'flat' structure or as a series of blocks laid one after the other in a line from left to right, the high-water mark (HWM) would be the rightmost block that ever contained data, as illustrated in Figure 10-1.
+---- high water mark of newly created table
|
V
+--------------------------------------------------------+
| | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
high water mark after inserting 10,000 rows
|
v
+--------------------------------------------------------+
|x |x |x |x |x |x |x |x |x |x |x |x | | | | | | | |
|x |x |x |x |x |x |x |x |x |x |x |x | | | | | | | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
high water mark after inserting 10,000 rows
|
v
+--------------------------------------------------------+
|x |x |x |x |x |x |x | | | | | | | | | | | | |
|x |x |x |x |x |x |x | | | | | | | | | | | | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 10-1. Depiction of an HWM
Figure 10-1 shows that the HWM starts at the first block of a newly created table. As data is placed into the table over time and more blocks get used, the HWM rises. If we delete some (or even all) of the rows in the table, we might have many blocks that no longer contain data, but they are still under the HWM, and they will remain under the HWM until the object is rebuilt, truncated, or shrunk (shrinki
相关文档：
'-------------------------------------------------------------------以下是登录代码
<%@ page contentType="text/html; charset=gb2312"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3 ......
声明：
以下的例子不一定正确，只是为了演示大概的流程。
一：无返回值的存储过程
存储过程为：
CREATE OR REPLACE PROCEDURE TESTA(PARA1 IN VARCHAR2,PARA2 IN VARCHAR2) AS
BEGIN
INSERT INTO HYQ.B_ID (I_ID,I_NAME) VALUES (PARA1, PARA2);
END TESTA;
然后呢，在java里调用时就用下面的� ......
自己在做这个程序的时候看过很多的资料，上网也查了不少的资料，可是多半说的是出神入化，云里雾里...不光看了不明白，而且是有明白一点的人，看了也变的有些模糊了。
这里我掩饰一套完整的java jdbc 连接Oracle9i的范例。
package com.lxh.dbcon;//打包
import ......
数学函数
在oracle 中distinct关键字可以显示相同记录只显示一条
1.绝对值
S:select abs(-1) value
O:select abs(-1) value from dual
2.取整(大)
S:select ceiling(-1.001) value
O:select ceil(-1.001) value from dual
3.取整（小）
S:select floor(-1.001) value
......
我在把oracle数据导入sqlserver中时，发现在oracle中字段定义为唯一索引时，不同记录的此字段如果为空不被认为是重复的，但在sqlserver中如果此字段为唯一索引字段，不允许有2个以上的空值。郁闷。所以只好将sqlserver中的唯一索引字段手工修改为几个非空的值，但这样程序肯定要进行修改了。需要在程序中为此字段设置不重复 ......
