Is my PHP optimum?

Dear Experts,

Is this the best way for me to generate a query which I will later execute to insert the data into the databases?

<?php
      $connection = mysql_connect('server', 'user', 'pass') or die (mysql_error());
      $db = mysql_select_db('database', $connection) or die (mysql_error());
      
      $query  = "Select DataID + 1 as NextID From tblData where DataID < 18581088 Order By DataID desc limit 1";
      $result = mysql_query($query) or die('Error, query `' . $query . '` failed');
      
      $row = mysql_fetch_array($result);
      extract($row);
      
      $the_heading = "the heading goes here";
      $the_date = "2008-06-26 00:00:00"';
      $the_content = "the content goes here";
      $the_categories = "4380138181,43830184182,43801558183,4380158184,43806518185,438418186";

      $generate_query = "insert into tblData ( Heading, Date, Contents, DataID ) values ( '$the_heading', '$the_date', '$the_content', $NextID );";
      
      $categories = explode(",",the_categories);
      
      for ($i=0;$i<count($categories);$i++){
            
            $query  = "select GroupName from tblIDLookup where DataID = $categories[$i]";
            $result = mysql_query($query) or die('Error, query `' . $query . '` failed');
            
            $row = mysql_fetch_array($result);
            extract($row);
            
            $generate_query .= "<br />insert into tblCat (DataID, CatID, CatName) values ($NextID, $categories[$i], $GroupName);";
      }
      
      echo $generate_query;
      
      mysql_close($connection);
?>

It does the following

1. Get the next id but ignore the higher number ids
2. The 4 variables $the_heading, $the_date, $the_content, $the_categories will be textboxes on the users screen which will be filled in by the user
3. I loop through the categories to get the category name from another table based on the exploded category ids, then generate the next query, this continues until all categores are found

I feel this is not very optimum and not using best practices.  Any suggestions for improvements?

When I say "improve" or "optimum", I mean is my code good practice, is it easy on the server, is it fast for the user to download etc etc.

Thanks.