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.
Caution:Security: the default character set
The character set must be set either at the server level, or with the API function mysql_set_charset for it to affect mysql_real_escape_string. See the concepts section on character sets for more information.
The string that is to be escaped.
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 had been called with no arguments. If no connection is found or established, an E_WARNING level error is generated.
Returns the escaped string, or false on error.
Exceptions and Errors
Executing this function without a MySQL connection present will also emit E_WARNING level PHP errors. Only execute this function with a valid MySQL connection present.
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.
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.
If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.
mysql_real_escape_string does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.