如何使用PHP检查数据库中是否存在用户

Question

SOLUTION: The the ending " after the SQL query was in the wrong place. and also declaring the $user and $password before the SQL query helped as well. Thanks all.

I am struggling to figure out why this does not work. To me it make perfect sense.

Also, I do know my code may be using old techniques and at risk for injection, this is just for a proof of concept.

Here is my code:

<?php
$db = mysql_connect("localhost", "root", "root");
if (!$db) {
die("Database connect failed: " . mysql_error());
}

$db_select = mysql_select_db("test", $db);
if (!$db_select) {
die("Database selection failed: " . mysql_error());
}

$username = $_POST['username'];

$result=mysql_query("SELECT * FROM Dbusers (username,pass) WHERE username,pass ='$username','$pass'");
if(mysql_num_rows($result) == 1) {

        header ("location: UniHelpindex.php");
}
else
{
    echo ("Login Details Wrong");
}

?>

Anything that my help let me know.

Answer 1

This is a syntax error:

WHERE username,pass ='$username','$pass'

You meant this:

WHERE username = '$username' AND pass = '$pass'

Also, where do you ever define $pass ? If you don't define it, then the SQL query may just be looking for an empty string which might not match any records (I hope).

---

When a query is failing, the system doesn't necessarily tell you outright. (Although in this case mysql_num_rows($result) is very likely throwing an error. Turn on error reporting, check your logs, etc.) Take a look at the mysql_error() function to check for errors any time mysql_query() returns false (which it does in the event of an error).

---

And, yes, insert the standard disclaimer here that you're using woefully outdated libraries and wide open to SQL injection.

Answer 2

我不确定，但是我认为您的SQL命令中的$ pass变量未定义。

Answer 3

don't use mysql_ it's depreciated. Use instead mysqli_

 $db=mysqli_connect('hostname','usrname','password','dbname')or die(<h2>some html code for showing the error</h2>);
$query="SELECT * FROM Dbusers WHERE username='$username' AND password='$password'";
$result=mysqli_query($db,$query);
if($mysqli_num_rows !=0){
//user was found stuff here 
}else{
//user not found stuff here
}
**I hope it helped**

Answer 4

解决方案：SQL查询后的末尾“放在错误的位置。并且在SQL查询之前也声明了$ user和$ password。同样，谢谢。

Answer 5

use a query like

SELECT pass from Dbusers WHERE username = '$username' LIMIT 1

This is very insecure though, please clean the data before using a query like this.