Phpmysql_real_escape_string function usage and instance tutorial

The mysql_real_escape_string () function is used to escape special characters in the strings used in SQL statements in unescaped_string. Considering the connection settings of the current character, it is safe in mysql_query () it. If binary data is to be inserted, this function must be used.

The following characters are affected:

• \ X00
• \ N
• \ R
• \
• '
• "
• \ X1a

If yes, the function returns the escaped string. If it fails, false is returned.

Syntax

mysql_real_escape_string(string,connection)

Parameters	Description
String	Required. Specifies the string to be escaped.
Connection	Optional. MySQL connection is required. If not specified, use the previous connection.

Description

This function escapes special characters in string and considers the connected current character set. Therefore, it can be safely used for mysql_query ().

Tips and comments

Tip: you can use this function to prevent database attacks.

Example

Example 1

The code is as follows:
$ Con= mysql_connect ("localhost", "hello", "321 ");
If (! $ Con)
{
Die ('could not connect: '. mysql_error ());
}

// Code for obtaining the user name and password

// Escape the 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 );
?>

Example 2
Database attacks. This example shows what will happen if we do not apply the mysql_real_escape_string () function to the user name and password:

The code is as follows:
$ Con= mysql_connect ("localhost", "hello", "321 ");
If (! $ Con)
{
Die ('could not connect: '. mysql_error ());
}

$ SQL = "SELECT * FROM users
WHERE user = '{$ _ POST ['user']}'
AND password = '{$ _ POST ['pwd']}' ";
Mysql_query ($ SQL );

// Do not check the user name and password
// Any content entered by the user, for example:
$ _ POST ['user'] = 'John ';
$ _ POST ['pwd'] = "'OR'' = '";

// Some code...

Mysql_close ($ con );
?>

The SQL query will be like this:

SELECT * FROM users
WHERE user = 'John' AND password = ''OR'' = '', which means that any user can log in without entering a valid password.

Example 3
The correct method to prevent database attacks:

The code is as follows:
Function check_input ($ value)
{
// Remove the slash
If (get_magic_quotes_gpc ())
{
$ Value = stripslashes ($ value );
}
// If it is not a number, enclose it with quotation marks.
If (! Is_numeric ($ value ))
{
$ Value = "'". mysql_real_escape_string ($ value )."'";
}
Return $ value;
}

$ Con= mysql_connect ("localhost", "hello", "321 ");
If (! $ Con)
{
Die ('could not connect: '. mysql_error ());
}

// Perform a safe SQL statement
$ 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 );
?>