mysql_query
mysql_result
MySQL Functions
PHP Manual

# mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5, PECL mysql:1.0)

mysql_real_escape_string — Escapes special characters in a string for use in a SQL statement

### Description

string mysql_real_escape_string ( string `$unescaped_string` [, resource `$link_identifier` ] )

Escapes special characters in the `unescaped_string` , taking into account the current character set of the connection so that it is safe to place it in a mysql_query(). If binary data is to be inserted, this function must be used.

mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a.

This function must always (with few exceptions) be used to make data safe before sending a query to MySQL.

### Parameters

`unescaped_string`

  The string that is to be escaped.

`link_identifier`

  The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If by chance no connection is found or established, an `E_WARNING` level error is generated.

### Return Values

Returns the escaped string, or `FALSE` on error.

### Examples

Example #1 Simple mysql_real_escape_string() example

`<?php
// Connect
$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')
OR die(mysql_error());
// Query
$query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",
mysql_real_escape_string($user),
mysql_real_escape_string($password));
?>`

Example #2 An example SQL Injection Attack

`<?php
// Query database to check if there are any matching users
$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";
mysql_query($query);
// We didn't check $_POST['password'], it could be anything the user wanted! For example:
$_POST['username'] = 'aidan';
$_POST['password'] = "' OR ''='";
// This means the query sent to MySQL would be:
echo $query;
?>`

The query sent to MySQL:

    SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''

This would allow anyone to log in without a valid password.

Example #3 A "Best Practice" query

Using mysql_real_escape_string() around each variable prevents SQL Injection. This example demonstrates the "best practice" method for querying a database, independent of the Magic Quotes setting.

`<?php
if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
// Connect
$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');
if(!is_resource($link)) {
echo "Failed to connect to the server\n";
// ... log the error properly
} else {
// Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.
if(get_magic_quotes_gpc()) {
$product_name = stripslashes($_POST['product_name']);
$product_description = stripslashes($_POST['product_description']);
} else {
$product_name = $_POST['product_name'];
$product_description = $_POST['product_description'];
}
// Make a safe query
$query = sprintf("INSERT INTO products (`name`, `description`, `user_id`) VALUES ('%s', '%s', %d)",
mysql_real_escape_string($product_name, $link),
mysql_real_escape_string($product_description, $link),
$_POST['user_id']);
mysql_query($query, $link);
if (mysql_affected_rows($link) > 0) {
echo "Product inserted\n";
}
}
} else {
echo "Fill the form properly\n";
}
?>`

The query will now execute correctly, and SQL Injection attacks will not work.

### Notes

> Note: A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and `FALSE` is returned. If `link_identifier` isn't defined, the last MySQL connection is used.

> Note: If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.

> Note: If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.

> Note: mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.

### See Also

- mysql_client_encoding()
- addslashes()
- stripslashes()
- The magic_quotes_gpc directive
- The magic_quotes_runtime directive

mysql_query
mysql_result
MySQL Functions
PHP Manual