What is the best way to index this left join?
Or is there a better way to handle this query to make indexing easier?
This query is being used to display comments for a page (postid).
Each comment has it's own unique id (parent.id) and each child comment (reply) the parent.id is stored in (child.topid).
SELECT parent.id, parent.username, parent.body, parent.dt, child.id, child.username, child.body, child.dt
FROM comments AS parent
LEFT JOIN comments AS child ON child.topid = parent.id
WHERE parent.postid = 12 AND parent.topid = 0 AND parent.active = 1
ORDER BY parent.id DESC, child.id DESC