php - Insert multiple checkboxes into table column -

i have table documents , part of docs being assigned category. table doc_list looks this:

create table `doc_list` ( `doc_id` int(11) not null,   `doc_title` varchar(50) not null,   `doc_content` text not null,   `doc_created` datetime not null,   `doc_updated` timestamp not null default current_timestamp,   `user_id` int(11) not null,   `cat_no` int(11) not null ) engine=innodb  default charset=utf16 auto_increment=122 ; 

i having manually assign cat_no (which category id) want apart of doc form submission:

    <form action="actions/newdocadd.php" method="post" id="rtf" name="">         <input type="text" name="doc_title" id="doc_title" required="required" placeholder="document title"/><br />           <?php           try{             $results = $dbh->query("select * cat_list order cat_title asc  ");          }catch(exception $e) {             echo $e->getmessage();             die();         }          $docs = $results->fetchall(pdo::fetch_assoc);          foreach($docs $docs){            echo '                <input type="checkbox" name="cat_no" value="2" id="cat_no">'.$docs["cat_title"].'<br><br>              ';}         ?>          <textarea name="doc_content" id="doc_content" placeholder="document content" style="display: none;"></textarea>                 <iframe name="editor" id="editor" style="width:100%; height: 600px;"></iframe>  <br><br>  <input onclick="formsubmit()" type="submit" value="create document" name="submit"/>          </form> 

now shows me categories , displays them checkboxes because documents can apart of more 1 category want tick boxes , submit them database.

here category table:

create table `cat_list` ( `cat_id` int(11) not null,   `cat_title` varchar(32) not null ) engine=innodb  default charset=utf16 auto_increment=5 ; 

assuming documents can have multiple categories:

first need group checkboxes array. can using same name brackets.

<input type="checkbox" name="cat_no[]" value="1" /> <input type="checkbox" name="cat_no[]" value="2" /> <input type="checkbox" name="cat_no[]" value="3" /> 

now when submit form, $_post['cat_no'] array containing checked values.

for proper database normalization, need new table called 'doc_category'. in table, have composite key of 'doc_id' , 'cat_id':

doc_id  | cat_id 1       | 1 1       | 2 1       | 3 

this signifies doc_id 1 belongs categories 1, 2, , 3.

the relationship documents categories called many-to-many relationship in databases, requires third table (intermediate).