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PHP : Function Reference : MySQL Functions : mysql_real_escape_string


Escapes special characters in a string for use in a SQL statement (PHP 4 >= 4.3.0, PHP 5, PECL mysql:1.0)
string mysql_real_escape_string ( string unescaped_string [, resource link_identifier] )

Example 1457. Simple mysql_real_escape_string() example

// Connect
$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')
   OR die(

// Query
$query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",

Example 1458. An example SQL Injection Attack

// Query database to check if there are any matching users
$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";

// 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 1459. 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.


if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
// Connect

$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');

is_resource($link)) {

"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),

mysql_query($query, $link);

       if (
mysql_affected_rows($link) > 0) {
"Product inserted\n";
} else {
"Fill the form properly\n";

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

Code Examples / Notes » mysql_real_escape_string

09-sep-2006 06:22

Would this be better?
functions quote_smart($value) {
if(is_array($value)) {
if(get_magic_quotes_gpc()) {
if(!array_map("is_number",$value)) {
else {
if(get_magic_quotes_gpc()) {
if(!is_number($value)) {
$value="'" . mysql_real_escape_string($value) . "'";
return $value;


well, smth like that
function escape_string ($string,$dbcon=false) {
  if(version_compare(phpversion(),"4.3.0")=="-1") {
  } elseif ($dbcon) {
  } else { return false; }


To: eddypearson at gmail dot com
If thing that, this is better:
$_POST  = array_map('mysql_real_escape_string', $_POST);
$_SESSION  = array_map('mysql_real_escape_string', $_SESSION);


To aide in the simplicity of things, I try and validate the information before it is even queried to the MySQL server.
For example. With usernames and passwords, I check for spaces. And ; signs. If either of these are in there, then the login request is ignored, since I do not allow either during registration.
So a simple attack like:
1 or 1=1
Isn't even sent. Instead a "Please check username / password and try again" message is displayed. I display the same message when the query is ignored as I do when an invalid login is parsed. As to not "challenge" the attacker. Make them think simply it was an invalide username/password, rather than a big deal like
die("Hacking attempt!!!");
You could very easily implement logging to keep track of malicious IP's and what-not as well.


The quote_smart() function in the "Best Practice" section does not quote any value which is all numeric. This will drop all zero's from the the lefthand side of a string. While this is intended to simplify the query string when storing numeric values this has a negative effect when trying to store strings which just so happen to be all digits. For instance some zip codes have one or more zero's on the lefthand side, and an MD5 hash may contain all numeric characters and the lefthand characters can be zero's. In these cases the lefthand zero's will be dropped.
I would simply drop the is_numeric() check. There's no reason to not quote numeric values.
// bad query created using the quote_smart() function
$qs = "UPDATE tbl SET zipcode=" . quote_smart('01234');
// UPDATE tbl SET zipcode=1234
// acceptable query created after dropping the is_numeric() check
$qs = "UPDATE tbl SET number=" . quote_smart('01234');
// UPDATE tbl SET number='01234'

admin of

The quote_smart function in the example above has no issues with losing leading zeros.
If the variable passed to it is numeric in nature then the variable is returned unchanged. This is fine as a number cannot be the source of an insertion attack.
If the variable passed to it is a numbic string (that is to say a string whose format is that of a number per the rules of is_numeric) then the variable is is also returned UNCHANGED.  This is also fine because even though the variable is a string, we've confirmed that it contains only numbers, with a possible '.', '+', '-', 'e' (for exponential notation), or 'x' if it's a number in hex.  None of these characters is a risk.
If the variable is a string and does not appear to be a number it is properly escaped.


The problem with this function returning an empty string instead of an escaped string seems to be related to the mysql lib versions installed on the server. On 3 servers, each with php 4.3.10, I had no problems on 2 of them, but got the empty string on the 3rd. The 2 that worked had versions 4.1.x and 4.0.x of mysql. The 3rd that did not work had 3.23.x
The failure also only occurred when I did not have a mysql connection set up before running the escape function. If I did DB::connect (using the PEAR DB object) before running the function, it worked, even if I didn't pass in the connection id. If I ran the function before DB::connect, then I got an empty string.
So, if you are getting an empty string, check your mysql lib version and check where you are connecting to the db in relation to calling the escape function in your code.


The function quote_smart provided will fail on the following kind of string
The is_numeric will return true and will treat it as number. When it's passed to mysql, mysql'll think that it's a double and will try to parse it. But this number is much larger than the maximum allowed double in mysql. Thus, mysql will complain.
The fix is to add is_finite check when checking if the argument is a number.


Quick update to example 1402.A, in the example no database is selected, and therefore the query won't work right. Here is a updated version with the database selected. If anyone has any thoughts on how to improve my selection method, please let me know.
if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
   // Connect
   $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');
   $select = mysql_select_db('mysql_name', $link);
   if(!is_resource($link)) {
       echo "Failed to connect to the server";
   } elseif(!$select) {
    echo "Failed to select database";
   } else {
       // Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.
       if(get_magic_quotes_gpc()) {
           if(ini_get('magic_quotes_sybase')) {
               $product_name        = str_replace("''", "'", $_POST['product_name']);
               $product_description = str_replace("''", "'", $_POST['product_description']);
           } else {
               $product_name        = stripslashes($_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, $link),
       mysql_query($query, $link);
       if (mysql_affected_rows($link) > 0) {
           echo "Product inserted\n";
} else {
   echo "Fill the form properly\n";


Of course, all of this is moot if you use the new (pdp 5.1) PDO class and PDO::prepare($sql) with bound variables that protects against sql injection.


Note that to use quote_smart(), you have to connect to the database via mysql_connect().  Otherwise, mysql_real_escape_string() will have no way of knowing what database you want to use.
If you want to use the OO approach or mysqli_connect(), you're going to have to rewrite quote_smart() to accept a MySQL connection, which it would then pass to mysql_real_escape_string().
This is a pretty lackluster solution, though, for anyone concerned with abstraction.


Note that mysql_real_escape_string doesn't prepend backslashes to \x00, \n, \r, and and \x1a as mentionned in the documentation, but actually replaces the character with a MySQL acceptable representation for queries (e.g. \n is replaced with the '\n' litteral). (\, ', and " are escaped as documented) This doesn't change how you should use this function, but I think it's good to know.

brian dot folts

mysql_real_escape_string is a bit annoying when you need to do it over an array.
function mysql_real_escape_array($t){
return array_map("mysql_real_escape_string",$t);
this one just mysql_real_escape's the whole array.
ex) $_POST=mysql_real_escape_array($_POST);
and then you dont have to worry about forgetting to do this.


just tried on php 4.4.2  the quote_smart example works just fine with 0666 it comes back as 0666 and 00 comes back as 00.  a single 0 gets lost however but I don't see that as a problem, unless of course you want that as your password. quote_smart works for me.


It's quite easy to stop the problem of 0666 returning as 666 in the example of quote_smart. Look at this:
// Quote variable to make safe
function quote_smart($value) {
  // Stripslashes
  if (get_magic_quotes_gpc()) {
      $value = stripslashes($value);
  // Quote if not integer
  if (!is_numeric($value) || $value[0] == '0') {
      $value = "'" . mysql_real_escape_string($value) . "'";
  return $value;
It now checks if there is a leading zero, and then it should be treated als a text, instead as a numerical value. Just an easy workaround.

kael dot shipman

It seems to me that you could avoid many hassels by loading valid database values into an array at the beginning of the script, then instead of using user input to query the database directly, use it to query the array you've created. For example:
//you still have to query safely, so always use cleanup functions like eric256's
$categories = sql_query("select catName from categories where pageID = ?",$_GET['pageID']);
while ($cts = @mysql_fetch_row($categories)) {
//making $cts both the name and the value of the array variable makes it easier to check for in the future.
//obviously, this naming system wouldn't work for a multidimensional array
$cat_ar[$cts[0]] = $cts[0];
//user selects sorting criteria
//this would be from a query string like '?cats[]=cha&cats[]=fah&cats[]=lah&cats[]=badValue...', etc.
$cats = $_GET['cats'];
//verify that values exist in database before building sorting query
foreach($cats as $c) {
if ($cat_ar[$c]) { //instead of in_array(); maybe I'm just lazy... (see above note)
 $cats1[] = "'".mysql_real_escape_string($c)."'";
$cats = $cats1;
//$cats now contains the filtered and escaped values of the query string
$cat_query = '&& (category_name = \''.implode(' || category_name = \'',$cats).'\')';
//build a sql query insert
//$cat_query is now "&& (category_name = 'cha' || category_name = 'fah' || category_name = 'lah')" - badValue has been removed
//since all values have already been verified and escaped, you can simply use them in a query
//however, since $pageID hasn't been cleaned for this query, you still have to use your cleaning function
$items = sql_query("SELECT * FROM items i, categories c WHERE i.catID = c.catID && pageID = ? $cat_query", $pageID);


if you're doing a mysql wildcard query with
you may use addcslashes to escape the string:
$param = mysql_real_escape_string($param);
$param = addcslashes($param, '%_');


I think instead of just using the quote_smart function to quote whatever the user gives you, you should ideally specify whether you are looking for a string or a number.  For example if you have a user script and are using a sql statement like this, where username is a char or varchar field:
$sql="SELECT id FROM user_table WHERE user_name=".quote_smart($_POST['userName']);
if the user submits 12345 for example, you get:
SELECT id FROM user_table WHERE user_name=12345
Your DB 1) Must convert the 12345 to a string (not a huge deal) 2) Probably cannot use any index you have on that column (could be a bigger deal with a sizeable table)
So i think something more along the lines of:
function quote_smart($val,$valType) and handle the input based on $valType (being either string or numeric)


I concur with icydee.  It's important that SQL Injection is prevented on the server side.  A person (or software) doing SQL Injection on your site will often post to your page from one of his own making.  For example, you may present a page like the following on that sanitizes all data before submitting.
<head><script type="text/javascript" src="validation.js" /></head>
 <form method="POST" action="/login.php">
 Name: <input type="text" name="the_acount" value="" /><br/>
 Password: <input type="password" name="pwd" value="" /><br/>
 <input type="submit" name="action" value="Submit" onClick="Sanitize()"/>
Your attacker views the source code and makes his own login page on his local hard drive.  It doesn't have to look like or even load from your page as long as he posts the form data to your site using your expected parameters.
 <form method="POST" action="">
 <input type="hidden" name="the_acount" value="1'; drop table users; select 1 where name='" /><br/>
 Password: <input type="hidden" name="pwd" value="Oh, was I supposed to be hashed?" /><br/>
 <input type="submit" name="action" value="Submit" />


Since SQL injection is such a fear it is beyond me as to why this hasn't been included yet.   I set this function up to take a query with ?'s in it and replace those with the correctly quoted values.  I don't do the "smart quoteing" i quote it in the SQL because i like to see the quotes there.
function db_query($query) {
 $args  = func_get_args();
 $query = array_shift($args);
 $query = str_replace("?", "%s", $query);
 $args  = array_map('mysql_real_escape_string', $args);
 $query = call_user_func_array('sprintf',$args);
 $result = mysql_query($query) or die('Query failed: ' . mysql_error());
 return $result;
call it like
$results = db_query("SELECT * FROM users WHERE username='?' AND password = PASSWORD('?');", $username,$password);
This automagicaly quotes them and executes the query for you and also dies if there is an error in the query.

23-jan-2006 03:03

Here's why pmioni is wrong:

keith dot lawrence

Here's my version, this replaces empty strings with NULLs instead of using a quoted empty string which was causing a sql error when adding empty values to an integer column which allows nulls. Your mileage may vary.
function quote_smart($value) {
if (get_magic_quotes_gpc()) $value = stripslashes($value);
if($value == '') $value = 'NULL';
else if (!is_numeric($value) || $value[0] == '0') $value = "'" . mysql_real_escape_string($value) . "'"; //Quote if not integer
return $value;

s. w.

For a "best practices" approach to handling user input, one should always include enforcement of input length limitations.  This will avoid potential attacks based on *very* large values being inserted, some of which may not be foiled just by escaping a string.  (Length limits imposed via your form may be bypassed by submitting from a page or tool created by the attacker.)  As a cursory example:
$maxNameLen = 25;
$limitedName = substr($_POST['username'],0,$maxNameLen);
$safeUsername = mysql_real_escape_string($limitedName);
Note that you'll need to take care to truncate the correct (raw) value and not something that has already been processed.  Otherwise, you're exposing the potential attack data to more potential points of failure, plus valid input may grow in length with escape processing and be incorrectly truncated.

aidan kehoe
eric256 at gmail dot com: the PEAR DB API provides exactly that. See


As for the example that uses empty instead of isset, keep in mind that "0" returns true for empty.  This may not be a good idea if a user_id could be 0.

cedric over blog com

as already said :
the example is wrong !
If your password is 0666 quote_smart will return : 666

tim furry

Another variant on quote_smart. I figured the problem with other versions (and I *do* use them) is that they're trying to *not* quote numbers; so I turned it around to check for the input value being a string instead.  Keep in mind that all incoming values via GET, POST, etc. are already strings.
This version provides correct quoting for leading zeroes and single-digit numeric zeroes (a fault of most other versions), and places the burden of type-checking on the caller where it belongs (the caller implicitly controls the quoting via the type of value submitted to the function).  All strings are quoted even if castable to a numeric type.  Any non-string values are examined for being numeric and returned unchanged if so; otherwise an error is returned.  I couldn't think of any real world scenarios where handling arrays, objects or booleans made sense (MySQL doesn't support any of these natively).
This version also has two optional parameters that accept a boolean for "nullify" (returns NULL for nulls/empty strings/unset values if true instead of a quoted empty string) and "conn" (database connection resource for the mysql_real_escape_string function if desired).  To skip the nullify parameter but use the conn parameter, send null for the second parameter in the call.
Hope it'll help someone else out.
function quote_smart($value = "", $nullify = false, $conn = null) {
 //reset default if second parameter is skipped
 $nullify = ($nullify === null) ? (false) : ($nullify);
 //undo slashes for poorly configured servers
 $value = (get_magic_quotes_gpc()) ? (stripslashes($value)) : ($value);
 //check for null/unset/empty strings (takes advantage of short-circuit evals to avoid a warning)
 if ((!isset($value)) || (is_null($value)) || ($value === "")) {
   $value = ($nullify) ? ("NULL") : ("''");
 else {
   if (is_string($value)) {
     //value is a string and should be quoted; determine best method based on available extensions
     if (function_exists('mysql_real_escape_string')) {
       $value = "'" . (((isset($conn)) && (is_resource($conn))) ? (mysql_real_escape_string($value, $conn)) : (mysql_real_escape_string($value))) . "'";
     else {
       $value = "'" . mysql_escape_string($value) . "'";
   else {
     //value is not a string; if not numeric, bail with error
     $value = (is_numeric($value)) ? ($value) : ("'ERROR: unhandled datatype in quote_smart'");
 return $value;


An update on Example 1428. A "Best Practice" query
if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
else {
echo "Fill the form properly\n";
The condition above will still put empty data into a database even though forms are empty. The condition should be corrected to code below. It checks empty fields in a form and handle errors.
if (!empty($_POST['product_name']) && !empty($_POST['product_description']) && !empty($_POST['user_id'])) {
else {
echo "Fill the form properly\n";


After reading through all the different versions I came up with this:
function quote_smart($value)
if( is_array($value) ) {
return array_map("quote_smart", $value);
} else {
if( get_magic_quotes_gpc() ) {
$value = stripslashes($value);
if( $value == '' ) {
$value = 'NULL';
} if( !is_numeric($value) || $value[0] == '0' ) {
$value = "'".mysql_real_escape_string($value)."'";
return $value;
This version is a little slower but it will recursively handle arrays.


According to the newsforge refered to by Picky, it is adviseable to run PREPAREd statements in order to avoid injection. Plus, I created a table that stores pre-defined prepared statements and a procedure that runs that query. That way it's possible to control more tighly what's to be queried.
Example in mysql5 lingo:
create sys_queries (
     name varchar(100), # query ID
     mysql_statement text, #
     primary key( name )
insert into sys_queries set name='search_users', 'SELECT * FROM users WHERE concat( username, name, email ) REGEXP ?';
delim $$
create sp_perform_query( _name varchar(100), _search_term varchar(255) )
       SELECT mysql_statement INTO _stat FROM sys_queries WHERE name = _name;
       IF _stat IS NOT NULL THEN
               SET @a = _stat;
               SET @b = _search_term;
               PREPARE s FROM @a;
               EXECUTE s USING @b;
       END IF;
delim ;
in PHP5, use mysqli to call the procedure, first arg is the query name, second, the search arg. Still don't know a good way to pass multiple arguments to mysql, so please let me know.


A quick function to mysql_real_escape_string every value in array (Think $_SESSION and $_POST guys).
This may be simple, and to some bloody obvious, but its useful little function, and I could find one on this page so:
function CleanArray($array) {
foreach ($array as $key => $value) {
$array[$key] = mysql_real_escape_string($value);
return $array;

ludvig dot ericson

A case where you do not need to escape is when you are about to compare the UI (User Input) with a database through MD5 hashes, infact if you do, the password stored in the database will not match the one in the request.
I had a living  hell trying to solve this in my earlier days, so I just wanted to enligthen any other newbies,
is sufficient escaping.


@ keith dot lawrence at jpmh dot co dot uk:
But an empty string is not per defenition NULL... usually you look for NULLable columns in your database on special occasions, so I think it's best to keep that apart...


// this doesn't do adding the quotes, checking for null, etc that the quote smart does, it simply sanitizes input and handles arrays recursively
function sanitize($input){
foreach($input as $k=>$i){

return $output;
// use: if you are going to use $_POST, $_GET, $_COOKIE or $_REQUEST, include the appropriate line first.


include ('includes/db.php');
if ( get_magic_quotes_gpc() ) {
   $_POST= array_map('stripslashes', $_POST);
$username= mysql_real_escape_string(trim($_POST['username']));
$password= mysql_real_escape_string(trim($_POST['password']));
$mdpwd= md5($password);
$sql= sprintf("SELECT COUNT(*) AS login_match FROM `users` WHERE `username` = '%s' AND `password`= '%s'", $username, $mdpwd);
$res= mysql_query($sql) or die(mysql_error());
$login_match= mysql_result($res, 0, 'login_match');
if ( $login_match == 1 ) {
   //logged in
} else {
// not logged in

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