How do I increment a value with mysql update query (php)

I have a query that looks like this:

$sql = "UPDATE tbl SET amt_field='amt_field+1' WHERE username='" .mysql_real_escape_string($_SESSION['username']). "'";
        mysql_select_db('db',$con);
        mysql_query($sql,$con);

I want to increment the value as easily as possible.

I have tried:

"UPDATE tbl SET amt_field='a开发者_开发技巧mt_field+1' WHERE

"UPDATE tbl SET amt_field='amt_field' + 1 WHERE

"UPDATE tbl SET amt_field='amt_field++' WHERE

I don't get error messages, but the value in my db does not increase either.

UPDATE tbl SET amt_field = amt_field + 1 WHERE ...

If you use the single quotes ', you're telling the enclosed value to be interpreted as a string You were probably thinking about the tick marks. This is also valid:

UPDATE tbl SET `amt_field` = `amt_field` + 1 WHERE ...

This must be used when the column (or table etc.) has a reserved name.

Hello did you initialize a new session. Below worked perfectly for me.

  public static function insert_search($pdo)
  {
    @session_start();
    $ip = $_SERVER['REMOTE_ADDR'];
    $username = $_SESSION['username'];
    //$username = self::username();
    $date = date('Y-m-d');
    //Adding the total searches for the logged in user 
    $query = $pdo->query("UPDATE  `users` SET  `total_searches` = `total_searches` +1 WHERE username = '$username'");
  }

/* What you could potentially do is the following.
Make sure if you're doing it the procedural way
you put @session_start(); at the top of the page */

@session_start();
$sql = "UPDATE tbl SET amt_field ='amt_field' +1 WHERE username ='" .mysql_real_escape_string($_SESSION['username']). "'";
        mysql_select_db('db',$con);
        mysql_query($sql,$con);