SQL injection _php Tutorial in PHP query login

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For example, the following login code:

if ($l = @mysql_connect (' localhost ', ' root ', ' 123 ')) or Die (' Database connection failed ');

mysql_select_db (' Test ');

Mysql_set_charset (' UTF8 ');

$sql = ' Select ' from test where username = "$username" and password = "$password";

$res = mysql_query ($sql);

if (mysql_num_rows ($res)) {

Header (' location:./home.php ');

}else{

Die (' input error ');

}

----------------------------@chenwei Black-eyed poet --------------------------

Note that the above SQL statement, there is a great security risk, if you use the following universal password and universal user name, then you can easily access the page:

1. $sql = ' SELECT * FROM test where username = "* * *" and password = "* * *" or 1 = "1";

Obviously, the universal password for this SQL statement is: * * * "or 1 =" 1

2. $sql = ' SELECT * FROM test where username = "* * *" UNION SELECT * FROM users/* and password = "* * *";

Forward slash * indicates that the following does not execute, MySQL support Union union query, so directly query out all the data; So the universal user name for this SQL statement is: * * * "UNION SELECT * FROM users/*

However, this injection is only for SQL statements in code, if $sql = "SELECT * FROM Test where username = $username and password = $password";

The above injection is at least useless, but the method is the same;

After using PDO, SQL injection can be completely avoided, and in this fast-developing era, the framework is rampant, without much consideration for SQL injection.

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