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MySQL Error injection principle analysis (count (), Rand (), GROUP by)0x00 questionshave been using the MySQL Database error injection method, but why the error?Baidu Google know a bit, found that everyone is the official website of the conclusion

See Summer snow on the winter of Rand () and srand () produce random number of summary, very good, study, and then have Baidu other people's results, the system summarizes. This article turns from Summer snow winter:

--rand (x) returns a random floating-point value of V, in the range between 0~1 (that is, 0--If an integer parameter x is specified, it is used as the seed value, and the same seed number will produce a repeating sequence. If the same seed value

The C language uses the rand () function to implement random (int m), randrandom The rand () function is a real random number generator, and srand () sets the random number seed for rand. If you did not call srand () before calling rand () for the

Rand and srand usageFirst, we need to have a general opinion on rand & srand: srand initializes random seeds, and rand generates random numbers. The following describes in detail.Rand (Random Number Generation)Header file: # includeDefine function:

Srand () is to provide seed for rand (). If srand inputs the same value each time, the random number generated each time is the same, Srand (N) For (10) Rand ()That is to say, using a fixed value as the seed is a disadvantage. The common practice is

first we have a general view of Rand&srand: Srand initializes random seeds, Rand generates random numbers, which are explained in detail below.  rand (generates random numbers) table header files: #include  define function: int rand (void) function

Usage of Rand and SrandFirst we have a general view of Rand&srand: Srand initializes random seeds, Rand produces random numbers, which are described in detail below.RAND (generating random numbers)Table header file: #include define function: int

The formula is as follows: RAND () * (y-x) + x As we learn about PHP, a random function, Rand or Mt_rand, can pass in a parameter that produces a random integer between 0 and a parameter, or it can pass in two parameters, producing a random

Random Number or matrix with uniform distributionSyntaxY = rand (N)Y = rand (m, n)Y = rand ([m n])Y = rand (M, N, P ,...)Y = rand ([m n p...])Y = rand (SIZE ())RandS = rand ('state ')DescriptionThe rand function generates an array composed of random