PHP mysql_real_escape_string() Function
 Complete PHP MySQL Reference
Definition and Usage
The mysql_real_escape_string() function escapes special characters in a
string for use in an SQL statement
The following characters are affected:
This function returns the escaped string on success, or FALSE on
failure.
Syntax
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mysql_real_escape_string(string,connection)
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| Parameter |
Description |
| string |
Required. Specifies the string to be escaped |
| connection |
Optional. Specifies the MySQL connection. If not specified,
the last connection opened by mysql_connect() or mysql_pconnect() is used. |
Tips and Notes
Note: Use this function to prevent database attack!
Example 1
<?php
$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
// some code to get username and password
// escape username and password for use in SQL
$user = mysql_real_escape_string($user);
$pwd = mysql_real_escape_string($pwd);
$sql = "SELECT * FROM users WHERE
user='" . $user . "' AND password='" . $pwd . "'"
// more code
mysql_close($con);
?>
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Example 2
Database attack. This example demonstrates what could happen if we do not use
the mysql_real_escape_string() function on the username and password:
<?php
$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
$sql = "SELECT * FROM users
WHERE user='{$_POST['user']}'
AND password='{$_POST['pwd']}'";
mysql_query($sql);
// We didn't check username and password.
// Could be anything the user wanted! Example:
$_POST['user'] = 'john';
$_POST['pwd'] = "' OR ''='";
// some code
mysql_close($con);
?>
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The SQL sent would be:
SELECT * FROM users
WHERE user='john' AND password='' OR ''=''
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This means that anyone could log in without a valid password!
Example 3
The correct way to do it to prevent database attack:
<?php
function check_input($value)
{
// Stripslashes
if (get_magic_quotes_gpc())
{
$value = stripslashes($value);
}
// Quote if not a number
if (!is_numeric($value))
{
$value = "'" . mysql_real_escape_string($value) . "'";
}
return $value;
}
$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
// Make a safe SQL
$user = check_input($_POST['user']);
$pwd = check_input($_POST['pwd']);
$sql = "SELECT * FROM users WHERE
user=$user AND password=$pwd";
mysql_query($sql);
mysql_close($con);
?>
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Complete PHP MySQL Reference
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