SQL query to get posts from multiple categories but not in a category

You had to use LEFT JOIN to simplify the stuff. By the way, the same can be accomplished using WP_Query and I actualy don’t understand why you don’t want to use it.

Also I’ve changed the way you write the query and I’ve not use the hardcoded $table_prefix for answer to be useful for others too. You can replace $wpdb-> with wp_ in $query if you want to.

I assume you have third category ID=1000 (see NOT IN part):

<?php
global $wpdb;
$query = "
SELECT ID, post_title
FROM $wpdb->posts
    LEFT JOIN $wpdb->term_relationships ON (ID = $wpdb->term_relationships.object_id)
    LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
WHERE $wpdb->term_taxonomy.taxonomy = 'category'
    AND $wpdb->term_taxonomy.term_id IN(15, 5)
    AND $wpdb->term_taxonomy.term_id NOT IN(1000)
    ORDER BY ID DESC
    LIMIT 0, 60
";
$results = $wpdb->get_results($query);
foreach($results as $result) {
    echo $result->ID;
    echo '<br />';
    echo $result->post_title;
    echo '<hr />';
}

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