Sorted it:
$values = $wpdb->get_col( “SELECT meta_value
FROM $wpdb->postmeta AS wppm
JOIN $wpdb->posts AS wpp
ON wppm.post_id = wpp.ID
WHERE wpp.post_author = $post_author
AND wppm.meta_key = ‘spt_cpdlog_points'”);
$cpdlogpoints = “” . array_sum($values) . “”;
For anyone who sees this in the future!