w***z
发帖数: 1848 | 1 【 以下文字转载自 Linux 讨论区 】
发信人: windz (风子), 信区: Linux
标 题: how to delete a file with NULL name in unix?
发信站: BBS 未名空间站 (Tue May 8 12:08:36 2007)
I accidentally create a file with null name in unix. if I do "ls -l", I can
see the entry but cannot see the file name. How can I delete it? |
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h*****n
发帖数: 439 | 2 NULL is defined as 0 in C/C++ |
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B*****g
发帖数: 34098 | 3 Oracle 9i
准备run
SELECT ...
FROM table1 a
WHERE a.col1 IS NULL
在col１上怎么建index?
已经知道
create ind_tab1_col1 ON table1( NVL(col1, 'NULL') )
极其不喜欢.
Thanks |
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c*****t
发帖数: 1879 | 4 不清楚 Oracle，不过 PostgreSQL 里面 null 也可以被 index （不过不是所有的
case）。PostgreSQL 里面的 GiST 就支持。
另外，也可以看看是否可以 index 某个 expression 。这种情况下就是
（column == NULL） = TRUE 的 LHS 。PostgreSQL 里支持。Oracle 也应该支持
的吧 |
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B*****g
发帖数: 34098 | 5 （column == NULL） = TRUE 基本上和NVL一样，都是function based index，俺门公
司不许用。我也不是说一定要用index，其它solution也行。也就是说一个xx M
records的table，要找col（应该是个date）是null的。
Thanks |
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j***3
发帖数: 142 | 6 【 以下文字转载自 Statistics 讨论区 】
发信人: j1123 (2134), 信区: Statistics
标 题: [Mysql] how to return NULL count in group by query
发信站: BBS 未名空间站 (Wed Jun 30 09:45:08 2010, 美东)
I have a table like this:
color size fruit
red big apple
red small apple
green big apple
yellow small orange
red small orange
when I do:
select color, size, count(*) group by color, size;
I got:
red big 1
red small 2
green big 1
yellow small 1
but what I need is to also return the NULL group count su |
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n********6
发帖数: 1511 | 7 谢谢回复.
我明白你的意思.
只是好奇:既然null不是一个值,=是运算符，如何赋值？ |
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g***l
发帖数: 18555 | 8 RANK就是排序啊，你NULL怎么排序，当然先把NULL替换掉再去排，插队肯定是不行的 |
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B*****g
发帖数: 34098 | 9 rank null as higher rank, then when value is null, do not display rank |
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g***l
发帖数: 18555 | 10 不行吧，CASE NULL THEN STH，很容易出错的，在加上一层RANK，一般对NULL RECORDS
都要分别处理的， |
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z**********8
发帖数: 2049 | 11 TABLE NAME, REGISTERS
ID, first_name, last_name
10, ,
11, tina, A
12, ,
13, Tom, B
SELECT *
FROM REGSITERS
WHERE first_name is not null and last_name is not null
result,
???
THANKS! |
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v***v
发帖数: 267 | 12 with a1 (ID1,ID2) as ( VALUES ('A', ''), ('B', NULL), ('C', 'A')) select *
from a1 where ID1 not in (select ID2 from a1)
就是想找id1不出现在id2里面的行
事先不知道id2里面有NULL
结果就一行都没选上 |
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c*********e
发帖数: 16335 | 13 with a1 (ID1,ID2) as ( VALUES ('A', ''), ('B', NULL), ('C', 'A')) select *
from a1 where ID1 not in (select ID2 from a1 where ID2 IS NOT NULL)
* |
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n****f
发帖数: 3580 | 14 试试:
where trim(email) is not null
email如果定义成char(n), 看上去空的也不是null的， 而是由'blank'字符。 |
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s*******y
发帖数: 558 | 15 thanks a lot
但是你们的解释还是没法说服我
我看到下面这样的解释 觉得比较明白叻
public class MyApp {
public static void makenull(java.util.ArrayList c) {
// c - is a new refference on object of ArrayList class
// value of c refference is same as in s
// so you have two reffeneces on same object
c=null; // here you make c (one of this refference) as null
}
public static void main(String[] args) {
java.util.ArrayList s = new java.util.ArrayList();
MyApp.makenull(s);
//s - is still reffere |
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Z**********4
发帖数: 528 | 16 最近想做一个applet去检测浏览器的版本，想调用Javascript来做
查了一下很多用JSObject的 但是问题就出来了
JSObject win=null;
try
{
win = JSObject.getWindow(this);
...
}
这是我的代码 但是getWindow总是返回null
然后后面就不行了
这段代码我放在applet的init函数里面
我上网查了下 这个竟然被当做一个bug报道sun site的bug base里面去了
我尝试了jre的多个版本 1.3.0 1.4.05 jre6Update24 都不行。。都要放弃了 |
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b******l
发帖数: 2 | 17 I tried:
if obj != NULL: do sth
if obj != Null: do sth
if obj: do sth
But all failed. Any comments?
Thanks! |
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D*******a
发帖数: 3688 | 18 this is about null segment selector, not null pointer.
segmentation fault is generally caused by accessing non-existant memory or
denied access. |
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b********g
发帖数: 404 | 19 小写的null是keyword，NULL是MS封装的 |
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b******n
发帖数: 592 | 20 end is not null, it points to *after* last item. you have to take care of
iterators when you modify stl container. Why do you need a list of iterators
.
and potentially dangerous?
defined doubly linked list and the initial value NULL for X elements. I
expect a stl based solution can achieve similar behaviour. |
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X****r
发帖数: 3557 | 21 gcc optimizes the second case to call puts() instead, which can't handle
NULL.
%s in printf isn't required to be able to handle NULL anyway, so just don't
do it. |
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X****r
发帖数: 3557 | 22 拜托，你看了我的贴没有啊。
我不是说了print("%s\n", NULL);被优化成puts(NULL);了吗。
%s本来就没有规定可以处理空指针，gcc怎么做都不算错，没什么好琢磨的。 |
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l******d
发帖数: 530 | 23 看了你的帖子，还有一点没懂：
printf("%s",NULL)（%S后没有\n）没有被优化成puts(NULL)，所以没有Seg. fault，
是这样子吗？ |
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X****r
发帖数: 3557 | 24 puts会在字符串最后输出\n，所以printf("%s",NULL)没法优化成puts(NULL)啊。 |
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l******d
发帖数: 530 | 25 偶像狠狠的鞭答我吧，我想了一圈又糊涂了
为什么会"%s\n"被优化NULL，而"%s"就不会呢。
我知道puts会在字符串最后输出\n，但在"%s\n"后面加个"\n"怎么就成了NULL呢？ |
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X****r
发帖数: 3557 | 26 因为对于任何str，printf("%s\n", str);等价于puts(str)，所以gcc作了优化，
这里正好str是NULL。printf("%s", str);并不等价于puts(str)，所以真正的
printf被调用了，而glibc里的printf是可以处理NULL的。
其实从第一贴开始我就在说这个，要是还不清楚的话我实在不知道该怎么讲了。 |
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g*****g
发帖数: 34805 | 27 Row key shouldn't be null. It's possible to get a row with all columns null
due to tombstone.
和 |
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w***z
发帖数: 1848 | 28 【 以下文字转载自 Linux 讨论区 】
发信人: windz (风子), 信区: Linux
标 题: how to delete a file with NULL name in unix?
发信站: BBS 未名空间站 (Tue May 8 12:08:36 2007)
I accidentally create a file with null name in unix. if I do "ls -l", I can
see the entry but cannot see the file name. How can I delete it? |
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x***d
发帖数: 227 | 29 Connecting two DTE devices together requires a null modem that acts as a DCE
between the devices by swapping the corresponding signals (TD-RD, DTR-DSR,
and RTS-CTS).
连接two DCE口，也用null modem 吗？ |
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j****j
发帖数: 270 | 30 If matrices A and B are related by X*A=B,
Ap is the orthonomal basis of null(A'), so A'*Ap=0
Bp is the orthonomal basis of null(B'), so B'*Bp=0
Then is there a relation linking Ap and Bp?
Thanks a lot |
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e*******e
发帖数: 1144 | 31 Consider X as a n*p matrix (n>p), if there exist an p*1 vector v such that X*v = 0, we know that X is rank-deficient, and v is in the null space of X.
My question:
if there exist an p*1 vector v, and elements of v is either +1 or -1, then what can I say about the matrix X? X is not only rank-deficient: there should be something more that because v is not an arbitrary vector but an vector of +1 and -1. In other world, the null space of X contains a vector whose elements are either +1 or -1.
Is t... 阅读全帖 |
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m*****e
发帖数: 13 | 32 Deal All,
I want to ask a stupid question about the null model fit statistics in proc
logistic. I want to get the -2LogL of the null model. I thought there are
two ways to do that.
1) Run the model without specifying any independent variable, i.e.
proc logistic data = mydata descending;model youtcome = /firth;run;
In the output, I found:
Model Convergence Status
Convergence criterion (GCONV=1E-8) satisfied.
-2 Log L = 38.858
2) Run the model by specifying independen |
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on
发帖数: 199 | 33
This is embarrasing..
The implicit assumption is that balls from A and B follow a normal
distribution with different means for their weights. With all the numbers
give earlier, we couldn't reject Null 1 or 2 with any typical significance
values. Why can't it be a null hypothesis? could anyone reform the problem
and/or point me what exactly I missed?
thanks |
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g***l
发帖数: 22 | 34 The choice of Null and alternative depends on your point of interest. You
always want a low probability (usually 0.05) to make a type I error (reject
the NULL when it is true.)
In your case, if you don't want to misclassify a "A" ball as a "B" ball,
then the hypothesis will be:
H0: Brand is A
Ha: Brand is B
as the prob. of type I error (misclassify a "A" ball as a "B" ball) is
usually controlled at 0.05 or etc.
and vice versa.
Of course it might not be a very good example as it implies a classif... 阅读全帖 |
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S*******1
发帖数: 251 | 35 WHEN ASSIGN score to each record, if a variable is null, how to give the
null a score. this is my q.
with |
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s**p
发帖数: 702 | 36 【 以下文字转载自 Money 讨论区 】
发信人: shop (shop), 信区: Money
标 题: 求she+ 注册链接，价钱好商量，请站内pm(null)
发信站: BBS 未名空间站 (Sun Jan 15 12:06:54 2012, 美东)
Xiexie |
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c*******t
发帖数: 1095 | 37 因为想取消OPT申请，正好USCIS告诉我差文件叫我在3天内寄过去，如果没有在规定时
间内寄过去则会给我寄封mail说我的status变成NULL和OPTIONS TO DO.
有人变成这样的么，有哪些OPTIONS？变成这样以后能否比如明年重新申请OPT而不交钱
（340刀）？ 对再次申请OPT有没有影响?
因为要取消OPT也要寄封信去，3天也不一定能收到。
谢谢 |
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f*****y
发帖数: 444 | 38 checked the strlen source code, it doesn't check the NULL pointer, why? |
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r*******y
发帖数: 1081 | 39 if no NULL, then trouble |
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d****o
发帖数: 1055 | 40 没有问题，因为我的head就是第一个node，没有空的head node.
所以返回NULL了。
你觉得他那本书有没有错？ |
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p*i
发帖数: 411 | 41 By default a call to printf("%s\n", p) is converted at compile time to puts(
p) (it's faster).
That's why printf("%s", NULL) will succeed, since it won't be converted (
missing '\n'). |
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d**e
发帖数: 6098 | 42 类似
class ListNode(int x) {
this.value = x;
this.next = NULL;
} |
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z*******g
发帖数: 224 | 47 【 以下文字转载自 THU 讨论区 】
【 原文由 achuang 所发表 】
I think this happened in Tsinghua.
NULL：一不浪漫，二不温馨，但是真实
一不浪漫，二不温馨，但是真实
我有个大学同班女同学叫洁。洁从湖南一个县城的一中来，聪明而勤奋。
按照T大的标准，洁是个很漂亮的女孩。我就不说什么大眼皮双眼睛之类的话
了，其实我也没仔细看过她，总之大一刚进校，洁是副班长，就有许多高班生
来我们班扶贫，教跳舞，帮我们熟悉北京的旅游点。自然，所有活动都是要洁
参加的。中间的种种故事，大家都明白，我就不说了。不过所有努力一概无效，
追求者们全都碰了壁。
国庆的时候真相大白，洁带了一个男生到我们宿舍，说这是我的高中同学，在
天津上学，来北京玩，这两天住在你们这里好吗。我们说：“好，好”。
我的第一印象，那个男生消瘦而苍白(湖南人很少有的苍白)，眼睛很大，目光
永远在洁的身上。
说了几句话，知道他和洁是初中同班，在高中一个是文科的第一，一个是理科
的第一。男孩的名字叫军。
那两天他们整天在外，深夜才回来。因此我们不大有和军聊天的机会，他似乎
也不喜欢同人交往。 |
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p****s
发帖数: 3184 | 48
Seems no better way.
In oracle, use NVL function to convert NULL into an empty string ''.
In DB2, use case statement instead. |
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S**n
发帖数: 11 | 49 【 以下文字转载自 swan 的信箱 】
【 原文由 swan 所发表 】
sql server 不支持直接的
alter table tableName
add anewcolumn columnType not null
这样的形式。
有alternative的法子吗？
谢！ |
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