php - Inserting an array into a relational table -

i have 3 tables:

• user_login
• doc_list
• user_cat_link_table

so creating new user , apart of form shows array of available categories pulled cat_list table.

i struggling along other form data update user_cat_link_table.

the script take id of new user , take id of category selected checkboxes array:

here input form:

 <form action="actions/add_emp.php" method="post">        <input type="text" name="user" placeholder="username" required="required"  /><br/>       <input type="text" name="pass" type="password" placeholder="password"/></label><br/>          <input type="text" name="firstname" id="name" required="required"                 placeholder="firstname"/><br />         <input type="text" name="lastname" id="email" required="required"                 placeholder="lastname"/><br/>         <input type="email" name="email" id="city" required="required"                 placeholder="email address"/><br/>         <input type="text" name="extension" id="extension" required="required"                 placeholder="extension number"/><br/>         <select name="title">             <option  selected disabled>please select job title...</option>              <option disabled></option>             <option disabled>helpesk:</option>             <option value="technical support advisor">technical support advisor</option>             <option value="deputy team leade">deputy team leader</option>             <option value="team leader">team leader</option>             <option value="incident resolution advisor">incident resolution advisor             </option>              <option disabled></option>             <option disabled>call centre:</option>             <option value="technical support advisor">technical support advisor</option>             <option value="">deputy team leader</option>             <option value="">team leader</option>              <option disabled></option>         </select>   <div id="checkboxlist" >     <?php         foreach($category $cat){      ?>      <input type="checkbox" value="<?php echo $cat["cat_id"]; ?>"             name="cat_no[]" id="box1"> <?php echo $cat["cat_title"]; ?></a><br>      <?php     }     ?> </div>          <input type="submit" value="add user" name="submit"/><br />     </form> 

i can see if print_r() or var_dump() getting results expect:

array ( [action] => id          [user] => test23wer3e4weret4essd          [pass] => test [firstname] => test          [lastname] => test          [email] => tes@test.com          [extension] => 1234          [cat_no] => array ( [0] => 69                              [1] => 70                              [2] => 71 )          [submit] => add user ) 

here form acts script insert data both user_login table (which works) part @ bottom trying insert join table having trouble with:

<? session_start(); session_regenerate_id(); if(!ini_get('date.timezone')) {     date_default_timezone_set('gmt'); }      if(isset($_post["action"])){     if(isset($_post['submit'])){     include_once'../../config.php';        $dbh = new pdo("mysql:host=$hostname;dbname=dashboardr",$username,$password);     $dbh->setattribute(pdo::attr_errmode, pdo::errmode_exception);       if(isset($_post['user']) && isset($_post['pass'])){         $password=$_post['pass'];         $sql=$dbh->prepare("select count(*) `user_login` `username`=?");         $sql->execute(array($_post['user']));      if($sql->fetchcolumn()!=0){      die("user exists");      }else{         function rand_string($length) {         $str="";         $chars = "subinsblogabcdefghijklmanopqrstuvwxyz                             abcdefghijklmnopqrstuvwxyz0123456789";         $size = strlen($chars);         for($i = 0;$i < $length;$i++) {         $str .= $chars[rand(0,$size-1)];     }      return $str;      }         $p_salt = rand_string(20);          $site_salt="subinsblogsalt";          $salted_hash = hash('sha256', $password.$site_salt.$p_salt);          $sql=$dbh->prepare("insert `user_login`                             (`id`, `username`, `password`, `psalt`,                              `firstname`, `lastname`, `email`, `extension`)                               values (null, ?, ?, ?, ?, ?, ?, ?)");         $sql->execute(         array($_post['user'], $salted_hash, $p_salt, $_post["firstname"],                $_post["lastname"], $_post["email"], $_post["extension"]));         print_r($_post);         die();          $docid = $dbh->lastinsertid();  $sql = "insert `user_cat_link_table`(`userid`, `cat_id`) values"; $values = ""; $params = [];  foreach($_post["cat_no"] $cat)  {      $values.= "(?, ?), ";     $params[] = $cat; // correct here     $params[] = $docid; }     $values = substr($values, 0, -2);     $sql.= $values;     $query = $dbh->prepare($sql);     $query->execute($params);             if ($dbh->query($sql)) {      }else{}      $dbh = null;     } //catch(pdoexception $e)  header ('location: ../list_doc.php?success=1');      }      }     } ?>