Must understand SQL knowledge
1. query Two External table connections
There are two tables A and B:
mysql> select * from A;+------+------+| id | Col1 |+------+------+| 1 | AA || 2 | BB || 3 | CC |+------+------+3 rows in set (0.00 sec)mysql> select * from B;+------+------+| id | Col2 |+------+------+| 2 | DD || 3 | EE || 4 | FF |+------+------+3 rows in set (0.01 sec)
1. Left join between table A and Table B
First, fi
InnoDB table is not defined, Primay key, Then each row is incremented by a 6-byte rowid, and if so, how there are 4-byte indexed fieldsQ: How do I understand the length offset list? A: The length offset list represents the length of each directory and its relative position.Now let's do an experiment to see the difference between them.CREATE TABLE Test1 (T1 varchar () DEFAULT NULL,T2 varchar () DEFAULT NULL,T3 char (Ten) DEFAULT NULL,T4 varchar () DEFAULT NULL) Engine=innodb DEFAULT charset=lati
statements are then described in a simplified set of data. Consider the following two datasets, noting that some elements are in a, not in B, and vice versa.
Set " A" set "B"
AA BB
-------- --------
Item 1 Item 3
Item 2 Item 4
Item 3 Item 5
Item 4 Item 6
Left OUTER JOINNow execute the following SQL statement (left connection, OUTER join):
SELECT * from A left OUTER JOIN B on AA =
PromotionFirst, create an active object under the current execution environment, then set the variable declared with Var to the active object's property (that is, add it to the active object) and assign it to undefined, and then define the function Also added to the active object.1 if (false) {2 var aa = 20;3 var bb = 30;4}5 6 function aa () {};7 function bb () {};8 9//var defined AA,
://www.cnblogs.com/mzwr1982/archive/2012/05/20/2509295.html
Use of closures reference: http://blog.csdn.net/sunlylorn/article/details/6534610
and http://www.cnblogs.com/rainman/archive/2009/05/04/1448899.html
In simple terms:
Because the returned function is assigned a variable, although the function destroys its execution environment at the end of the execution,
However, if there is a closure, the closure saves the active object (variable) of the external function, so if you do not remove
involves reasoning and storage at the same time, when a person is learning to be stored in the mind, the essence is human. A different angle. From artificial intelligence, the computer is stored in the human learning and design indirectly reflect people's learning and reasoning, stored in the computer method. Learning and reasoning can be carried out first in the human mind, again put into the computer stored in the process, but also in the computer according to the design of people in the intr
The Nginx server searches multiple location blocks in the server block for a standard URI and a request string match, and if there are multiple matches, record the one with the highest matching degree. The server then matches the regular URI in the location block with the request string, and when the first regular URI matches successfully, ends the search and uses the location block to process the request, or if the regular match fails all, This request is processed using the most matching locat
0. stack unwinding. when an exception is thrown and control passes from a try block to a handler, the C ++ run time CILS Destructors for all automatic objects constructed since the beginning of the try block. this process is calledStack unwinding.
Two notes: 1) local objects will be destructed in reverse order; 2) if another exception thrown during stack unwinding in destructing an object, as no one can handle that exception, terminate will be called to end the program.View code
Class
uint32
for; J i + + uint32 (B[j]) }
Return
}
Func buildshadowheader (length UInt32) (b [8]byte) {
var i int
for; I B[i] = Flag[i]
}
A: = uint32tobytes (length)
for; I B[i] = a[i-4]
}
Return
}
Func Writeshadow (b []byte, im image. Image) (out image. Image, err Error) {
Max: = im. Bounds (). Max.x*im. Bounds (). MAX.Y/8-64
B_len: = Len (b)
If Len (b) > Max {
return nil, errors. New ("Image does not have enough spaces for shadow.")
}
Head: = Buildshadowheader (UInt32 (B_len))
v
Oracle
Sql> select * from AA;
BB CC--------------------1 999999.99
sql> col bb format ' 99.9 '; Sql> select * from AA;
BB CC---------------1.0 999999.99
Sql> Col bb head ' 99.9 '; Sql> select * from AA;
99.9 CC---------------1.0 999999.99
Sql> Col BB Head ' School Numb
= Detpath.format (classname) with open (Detfile, ' R ') as F:lines = F.readlines () splitline s = [X.strip (). Split (') for x in lines] Image_ids = [x[0] for x in splitlines] confidence = Np.array ([float (x[1]) for x in Splitlines]) BB = Np.array ([[Float (z) for z in X[2:]] "for X" Splitlines]) # Sort by confidence Sorted_ind = Np.argsort (- Confidence) BB = Bb
Compare the following two examples:Example 1:A=10b=aa=a+2print "A=", A, "b=", bResults: a= b= 10After a+2, B is still 10Example 2:Aa=[1,2,4]bb=aaaa.append (3) print "aa=", AA, "bb=", BB Results: aa= [1, 2, 4, 3] bb= [1, 2, 4, 3]AA adds an element of 3, BB also adds an eleme
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Now I want to retrieve all fields in Table AA. The condition is that the id value of AA is not in the ID value of BB ). That is, all fields with an odd ID are returned.
Use not inSQL:
Select * from AA where id not in (select ID from BB)
Just one statement is simple and clear, but it is a pity that the efficiency is not high, and the company's regulatory requirements do not need not i
conversion table. If the IP packet is not found, the host sends an ARP broadcast packet, the host refreshes its ARP cache. Then the IP package is sent out.
After learning this knowledge, we can now talk about how to implement ARP spoofing In the Ethernet. Let's look at this example.
3.1 ARP spoofing for the same network segment
Figure 2 ARP spoofing for the same network segment
As shown in figure 2, three hosts
A: IP address 192.168.0.1 hardware address AA: AAB: IP address 192.168.0.2 hardware
What is the JavaScript parsing mechanism? The JavaScript parsing process is divided into two stages, one is the compilation phase and the other is the execution phase. * Compile Phase The compile phase is what we often call the JavaScript pre-parsing (preprocessing) phase, in which the JavaScript interpreter will complete the conversion of JavaScript script code to bytecode. * Implementation phase In the compile-time JavaScript interpreter uses the execution environment to generate mechani
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