Ok, well I stumbled across this by sending a copy of the attempted SQL error to my email on a fail, this was due to a totally unrelated issue and it did help me correct the other issue. But in having that setup I found I received a lot of emails with the following content:
[CODE]SELECT thread.*,
thread_watch.email_subscribe
,
user.*, IF(user.username IS NULL, thread.username, user.username) AS username,
node.title AS node_title, node.node_name,
NULL AS thread_read_date,
0 AS user_post_count,
permission.cache_value AS node_permission_cache,
last_post_user.avatar_date AS last_post_user_avatar_date, last_post_user.gravatar AS last_post_user_gravatar, last_post_user.gender AS last_post_user_gender
FROM xf_thread_watch AS thread_watch
INNER JOIN xf_thread AS thread ON
(thread.thread_id = thread_watch.thread_id)
LEFT JOIN xf_user AS user ON
(user.user_id = thread.user_id)
LEFT JOIN xf_node AS node ON
(node.node_id = thread.node_id)
LEFT JOIN xf_permission_cache_content AS permission
ON (permission.permission_combination_id = 1
AND permission.content_type = 'node'
AND permission.content_id = thread.node_id)
LEFT JOIN xf_user AS last_post_user ON
(last_post_user.user_id = thread.last_post_user_id)
WHERE thread_watch.user_id = ?
AND thread.discussion_state = 'visible'
AND thread.last_post_date > 1411933660
AND thread.last_post_date > COALESCE(thread_read.thread_read_date, 0)
AND thread.last_post_date > COALESCE(forum_read.forum_read_date, 0)
ORDER BY thread.last_post_date DESC[/CODE]
This was on a version 1.3.5 install, however I posted the error only because I see the same function declaration in 1.4.2 with no changes.. I haven't setup the same email notification in a 1.4.2 install so it's entirely possible it's no longer an issue. But thought it worth bringing to your attention.
