我想编码我的数据库中是否已存在数据

i Just want code for if veriable $absolute_url value is already exist in mysql then show me a message i just want this Thank you..

$_SESSION['varname'] = $absolute_url;

$mailingwork = mysql_connect("localhost","root","");
mysql_select_db("inbox",$mailingwork);
if(isset($absolute_url) && !empty($absolute_url))
{
mysql_query("Insert Into deliveredinbox(mailerss) value('$absolute_url')");
    }

I think you just want to check if the $absolute_url already exists in the deliveredinbox table. If so, you can do a select query as follows to count the number of rows where the absolute url is equal to the url that you want to enter to the table.

if(isset($absolute_url) && !empty($absolute_url)){
    $count=mysql_query("SELECT count(*) from deliveredinbox where mailerss='$absolute_url'");
    mysqli_fetch_array($count);
    if($count[0]>0){
        //already exists
        echo "The url already exists";
    }   
    else{
        mysql_query("Insert Into deliveredinbox(mailerss) value('$absolute_url')");
    }
}

Try if (isset($absolute_url)) { your code here; }. It's not precisely the right tool, but I think that it will do the trick for you.

http://php.net/manual/en/function.isset.php.

Others are absolutely right about transitioning from old mysql calls in PHP. mysqli calls are more secure. PDO will save you time in coding and are even more secure.