Dupe-R-Scooper: prevent duplicate content

I hope this is the right place to post this.
I have been working back and forth with nevets over in the post installation support forum to develop a function to be used as a module to check titles and fields in custom content types when nodes are created. You can see the thread at http://drupal.org/node/89599. Unfortunately, I've been cluttering-up the thread over there with my posts so I figured I had better start my own thread to keep things more organized.

nevets had written a nice little function that checked for duplicate titles for nodes of a specific type. I wanted to do a more robust version, and he really helped me out in with my issues (I'm really new to PHP). I'm calling the new function "Dupe-R-Scooper" since it tries to scoop-up duplicate data before it gets published.

Anyway, long story short, I'd like to get a little help with the function, and get this developed into a full module with an admin-area UI.

The basic overview of the function is this:
1) we hook nodeAPI to catch the validate operation
2) we use a switch to check a number of node types
3) we run a query to pull specified fields and node title/nid from the {node} and {content_type_*} tables.
*3b) I need to somehow write a loop here to make sure we check everything that could be a match (but don't know how).
4) we run a few if() conditions against the new and existing data
5) if we get the proper matches, meaning the data already exists, we return a form_set_error() on the field with a friendly message.

So here is the code so far. Everything works without errors, I just don't have the loop written to make sure we're checking everything or just the first found data. that's where I need the help right now. I've generalized the type and field names.

<?php
// $Id: duperscooper.module,v 0.1.0 2007/10/11 ZrO-1 Exp $

/**
 * Dupe-R-Scooper implements the nodeAPI hook - duperscooper_nodeapi()
 * This function is to help reduce the number of duplicate or equivalent nodes of a particular type in our system.
 */

function duperscooper_nodeapi(&$node, $op) {
  if ( $op == 'validate' ) {
    switch ($node->type) {
      case 'mytype1':  // set this to your machine-readable type (we want to check title and 1 field for this type)
        $sql = "SELECT f.field_my_field_value, n.title, n.nid
                    FROM {node} n JOIN {content_type_mytype1} f USING(nid)
                    WHERE type = '%s' OR title = '%s' OR field_my_field_value = '%s'";
        $results = db_query($sql, $node->type, $node->title, $node->field_my_field[0]['value']);
        $existing = db_fetch_object($results);

        if (!$node->nid || $existing->nid != $node->nid) {  // if the node is new, OR we're not updating/editing an existing node
          
          if ($existing->title == $node->title) {                   // if an existing title matches the new title
            $link = l('view the existing '.$node->type, 'node/'.$existing->nid, NULL, NULL, NULL, FALSE, FALSE);
            form_set_error('title', 'Oops! There is already a '.$node->type.' called '.$node->title.'. Here is a link to '.$link.'. Please be absolutely sure that you are not creating a duplicate '.$node->type.'. Thanks!');
          }
          
          if ($existing->field_my_field_value == $node->field_my_field[0]['value']) {  // if an existing field matches the new field
            $link = l('view the existing '.$node->type, 'node/'.$existing->nid, NULL, NULL, NULL, FALSE, FALSE);
            form_set_error('field_my_field', 'Oops! There is already a '.$node->type.', called '.$node->title.', with the value '.$existing->field_my_field_value.'. Here is a link to '.$link.'. Please be absolutely sure that you are not creating a duplicate '.$node->type.'. Thanks!');
          }
        }
        break;

      case 'mytype2':  // set this to your machine-readable type (we want to check a combo of title and 2 fields for this type)
        $sql = "SELECT f.field_first_field_value, f.field_second_field_value, n.title, n.nid
                    FROM {node} n JOIN {content_type_mytype1} f USING(nid)
                    WHERE type = '%s' OR title = '%s' OR field_first_field_value = '%s' OR field_second_field_value = '%s'";
        $results = db_query($sql, $node->type, $node->title, $node->field_first_field[0]['value'], $node->field_second_field[0]['value']);
        $existing = db_fetch_object($results);

        if (!$node->nid ||  $existing->nid != $node->nid) {  // if the node is new, OR we're not updating/editing an existing node
          // if an existing title matches the new title AND an existing first_field matches the new first_field
          if ($existing->title == $node->title && $existing->field_first_field_value == $node->field_first_field[0]['value']) {
            $link = l('view the existing '.$node->type, 'node/'.$existing->nid, NULL, NULL, NULL, FALSE, FALSE);
            form_set_error('field_first_field', 'Oops! There is already a '.$node->type.' called '.$node->title.' with first_field value. Here is a link to '.$link.'. Please be absolutely sure that you are not creating a duplicate '.$node->type.'. Thanks!');
          }
          // if an existing title matches the new title AND an existing second_field matches the new second_field
          if ($existing->title == $node->title && $existing->field_second_field_value == $node->field_second_field[0]['value']) {
            $link = l('view the existing '.$node->type, 'node/'.$existing->nid, NULL, NULL, NULL, FALSE, FALSE);
            form_set_error('field_second_field', 'Oops! There is already a '.$node->type.' called '.$node->title.' with second_field value. Here is a link to '.$link.'. Please be absolutely sure that you are not creating a duplicate '.$node->type.'. Thanks!');
          }
        }
        break;
    }
  }
}
?>

So there are more cases in my particular application of this function, but I think the above example gives you a good idea of what I'm trying to accomplish.
Goal 1 for me is to get the checks looped so i can be sure we're checking everything
and a distant goal 2 for me is to get the function fully generalized and a UI built for this where an admin could check-off the content types and fields that they want to check and those selections get passed to the function.

I look forward to hearing from you guys.