hey i have registration form that has checkboxes along with other fields. i cant insert the selected checkbox values into the data base. i have made one field in the database for storing all checked values. this is the code for checkbox part in the form:

 Websites, IT and Software    Writing and Content 

          <pre><input type="checkbox" name="expertise[]" value="Design and Media"> Design and Media            <input type="checkbox" name="expertise[]" value="Data entry and Admin"> Data entry and Admin </pre>
          <pre><input type="checkbox" name="expertise[]" value="Engineering and Skills"> Engineering and Science     <input type="checkbox" name="expertise[]" value="Seles and Marketing"> Sales and Marketing </pre>
          <pre><input type="checkbox" name="expertise[]" value="Business and Accounting"> Business and Accounting     <input type="checkbox" name="expertise[]" value="Others"> Others </pre>

and this is the corresponding php code for inserting data

$checkusername=mysql_query("SELECT * FROM freelancer WHERE fusername='{$_POST['username']}'");

if (mysql_num_rows($checkusername)==1)
{
    echo "username already exist";
}
else
{
    $query = "insert into freelancer(ffname,flname,fgender,femail,fusername,fpwd,fphone,fadd,facc,facc_name,fbank_details,fcity,fcountry,fexpertise,fprofile,fskills,fhourly_rate,fresume) values 

('".$_POST['first_name']."','".$_POST['last_name']."','".$_POST['gender']."','".$_POST['email']."','".$_POST['username']."','".$_POST['password']."','".$_POST['phone']."','".$_POST['address']."','".$_POST['acc_num']."','".$_POST['acc_name']."','".$_POST['bank']."','".$_POST['city']."','".$_POST['country']."','".implode(',',$_POST['expertise'])."','".$_POST['profile']."','".$_POST['skills']."','".$_POST['rate']."','".$_POST['resume']."')";

   $result = 

($query) or die (mysql_error());

this code inserts data for all fields but the checkbox value field remains empty???