Exclude category from custom search

I’m running a couple of custom queries on custom post templates, and can’t figure out how to exclude a specific category from results.

In my database, in the wordpress_posts table, all the “post_category” fields are 0. However, the posts are in their own categories, and working right. So I’m not sure where the category gets saved.

I’m using this query:

$querystr = "
    SELECT DISTINCT wordpress_posts.*
    FROM $wpdb->posts wordpress_posts
    WHERE wordpress_posts.post_content LIKE '%$first_name $last_name%'
    AND wordpress_posts.post_status = 'publish'
    AND wordpress_posts.post_type = 'post'
    ORDER BY wordpress_posts.post_date DESC

I’m defining first_name and last_name from custom fields in WordPress.

I’ve tried:

$querystr = "
    SELECT DISTINCT wordpress_posts.*
    FROM $wpdb->posts wordpress_posts
    WHERE wordpress_posts.post_content LIKE '%$first_name $last_name%'
    AND wordpress_posts.post_category != '1302'
    AND wordpress_posts.post_status = 'publish'
    AND wordpress_posts.post_type = 'post'
    ORDER BY wordpress_posts.post_date DESC

But that didn’t work. Can someone point me in the right direction? (which, with my luck, is right in front of my face)