i make PHP site  With USER / Pass Login  But USer can Skip This Page BY Use '=' 'or' ‘ or 1=1  Like this  Code Here In File Login_Check.php  `  include("includeszzz/host_conf.php"); include("includeszzz/mysql.lib.php"); $obj=new connect; $obj1=new connect; $username=$_GET["username"]; $password=$_GET["password"]; //echo $username; //echo $password; $sql="select username from  admin where username='$username'"; $obj-&gt;query($sql); $U_num=$obj-&gt;num_rows(); //echo $U_num; if($U_num!=0) { $sql1="select password from admin where username='$username' and password='$password'"; $obj1-&gt;query($sql1); $P_num=$obj1-&gt;num_rows();     if($P_num!=0) {         session_start();         $_SESSION["zizo"]="$username";     //header("location: welcome.php");     echo "1"; } else {     echo "Invalid Password Please Try Again"; } }  else { echo "Invalid Username Please Try Again"; }   `
If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?
Where can I find out about Stack Overflow history? I'd like to know how Stack Overflow and other sites started - which was first, who initiated it (OK, that's on the link below) and why, how the different sites evolved, how the rules evolved, etc.  Where can I find such information?  Of course, I know I can look at  for a brief overview but I'm wondering if there is info on this site, particularly more detailed.. Applications Not Reopening After Restart How discontinuous can a derivative be? There is a well-known result in elementary analysis due to Darboux which says if $f$ is a differentiable function then $f'$ satisfies the intermediate value property.  To my knowledge, not many "highly" discontinuous Darboux functions are known--the only one I am aware of being the Conway base 13 function--and few (none?) of these are derivatives of differentiable functions.  In fact they generally cannot be since an application of Baire's theorem gives that the set of continuity points of the derivative is dense $G_\delta$.  Is it known how sharp that last result is?  Are there known Darboux functions which are derivatives and are discontinuous on "large" sets in some appropriate sense? Homework - set theory infinite union A question from my homework I'm having trouble understanding. We are given:  $A(1) = \{\varnothing\}$, $A(n+1) = A(n)\cup (A(n)\times A(n))$  $A=A(1)\cup A(2)\cup A(3)\cup \cdots \cup A(n)\cup A(n+1) \cup \cdots$ to infinity  The questions are:  1) show that $A\times A \subseteq A$  2) Is $A \times A = A$?  Thank you for your help.  I've tried writing $A(2)$ but it gets really complicated and I'm having trouble understanding what the sets are. Let alone solve the question. I've been reading through a lot of the rookie Java questions on finalize() and find it kind of bewildering that no one has really made it plain that finalize() is an unreliable way to clean up resources.  I saw someone comment that they use it to clean up Connections, which is really scary since the only way to come as close to a guarantee that a Connection is closed is to implement try (catch) finally.    I was not schooled in CS, but I have been programming in Java professionally for close to a decade now and I have never seen anyone implement finalize() in a production system ever.  This still doesn't mean that it doesn't have its uses, or that people I've worked with have been doing it right.  So my question is, what use cases are there for implementing finalize() that cannot be handled more reliably via another process or syntax within the language?    Please provide specific scenarios or your experience, simply repeating a Java text book, or finalize's intended use is not enough, as is not the intent of this question. Time limited and band limited signal Constant Amortized Time What is meant by "Constant Amortized Time" when talking about time complexity of an algorithm? How do I hide javascript code in a webpage? Proof of Dobinski's formula for Bell numbers How would I solve the following problem involving elementary matrices? Let $A=\begin{pmatrix}0&amp;5\\ 7&amp;4\end{pmatrix}$.      1) Write $A$ as a product of $4$ elementary matrices.      2) Write $A^{-1}$ as a product of $4$ elementary matrices.   My work. I have managed to find $A^{-1}$, which came out to be this:  \begin{pmatrix}-\frac{4}{35}&amp;\frac{1}{7}\\ \frac{1}{5}&amp;0\end{pmatrix}  However, I am struggling to figure out how I would split each of these matrices into $4$ elementary matrices. Any help? Some time ago, I baked a cake (Sachertorte to be exact). The taste and texture was fine, so my recipe is okay.  My biggest issue was the shape. In the middle it was really a lot higher than on the sides. I would like to redo it in the near future, but preferably with a flat(ter) surface. (Especially since I put icing on top and I don't want it to drip off this time.)  Anyone knows the cause of my problem, or even better a solution? I think I put enough butter on the side of my springform pan, in case this is an option. Both DHCP and static IP addresses simultaneously on one interface We can use multiple IP addresses for a single interface in Linux (eg. eth0:0, eth0:1). But can we use DHCP and static IP at the same time? eth0:1 should have a static IP address and eth0:0 should be configured using DHCP.  How can we accomplish both? What is object serialization? I know on client side (javascript) you can use windows.location.hash but could not find anyway to access from the server side. I'm using asp.net. How can I make sure that a certain OLEDB driver is installed when I start my application? I use ADO from Delphi and would like to display a descriptive error message if the driver is missing. The error that's returned from ADO isn't always that user-friendly.  There are probably a nice little function that returns all installed drivers but I haven't found it. How can I move my /home directory to another partition if it's already part of the / partition? I have a wonderful running Maverick Meerkat install going on right now. I want to move my /home to another partition as per many suggestions.   How can I go about doing this without reinstalling the entire Ubuntu system? Can I simply create the partition with gparted and then change the mount point of /home in fstab to reflect it or is it a bit more difficult? I have a proof and need some feedback. It seems really obvious that the statement is true but it is always the obvious ones that are a little trickier to prove. So I would appreciate any feedback. Thank you!  Here is what I am asked to prove:     If $n$ is composite then $(n-1)! \equiv 0 \pmod n$.   Proof:  $n$ is composite $\implies n=ab$ where $a,b \in \mathbb{Z}$ and $0&lt;a,b&lt;n$.  Case 1: If $a=b$ then $n=a^{2}$. Now $n \mid (n-1)! \implies a \mid (n-1)!$, so $$\begin{aligned} (n-1)! &amp;\equiv 1\times 2\times \dotsb \times a \times\dotsb\times (n-a)\times\dotsb\times (n-1) \\ &amp;\equiv 1\times 2\times \dotsb\times a \times\dotsb\times -a\times\dotsb\times -1 \\ &amp;\equiv 0 \pmod n \end{aligned}$$  Case 2: $0&lt;a&lt;b&lt;n$.  Then, since $a \mid n$, $b \mid n$ and $n \mid (n-1)!$ we have that $a \mid (n-1)!$ and $b \mid (n-1)!$.  So this implies $(n-1)! \equiv 1\times 2\times \dotsb\times a \times\dotsb\times b\times\dotsb\times (n-1) \equiv 0 \pmod n$, Q.E.D. Why must the eigenvalue of the number operator be an integer? My apologies if this question has already been answered. Using the notation of Sakurai, we have an energy eigenket N and an eigenvalue n.  $$N | n \rangle = n | n \rangle$$  For the number operator $N = a^\dagger a $. My question is precisely why does n have to be an integer. I do understand that it must be positive definite due to the norm condition on $ a | n \rangle $:  $$\langle n | a^\dagger a | n \rangle \geq 0$$  I can see that we can show:  $$ a | n \rangle = \sqrt{n-1} | n-1 \rangle $$ and similarly for $a^\dagger | n \rangle$  Sakurai argues that the sequential operation of $a$ operators leads to the form which he does not write, but I will write here for clarity:  $$ a^k | n \rangle = \left(\sqrt{n}\sqrt{n-1}...\sqrt{n-k+1}\right) | n - k + 1 \rangle $$   Since  $$ a|0 \rangle = 0 $$  the sequence must terminate, but can only terminate if n is an integer. How can we make that jump? Is there a formal mathematical proof that the sequence $\left(\sqrt{n}\sqrt{n-1}...\sqrt{n-k+1}\right)$ will terminate if and only if n is an integer? Samba+Windows: Allow multiple connections by different users? I have a machine running Ubuntu with Samba that I use to share stuff with my family's Windows machines in our local network.  Currently they access a share for movies/music/etc with one user.  I want to connect them to another share as a different user (for example, user "goytacaz").  When I try connecting to this new share, Windows gives me "Error 1219" and complains about multiple connections by the same user.  How do I get my machine to accept multiple connections by the same user? Can I use images rendered with blender for commercial use? If I make a scene and then render it with BR or Cycles, am I allowed to use that image in a commercial project? Do I need to include any copyright notice or license?