(SELECT *
FROM `dozhan_reply` t1
WHERE `reply_parent` IN (
SELECT `reply_id`
FROM (
SELECT `reply_id`
FROM `dozhan_reply`
WHERE `reply_article` = 69
AND `reply_type` = 0
LIMIT 0, 5
) t
))
UNION
(SELECT *
FROM `dozhan_reply`
WHERE `reply_article` = 69
AND `reply_type` = 0
LIMIT 0, 5)
UNION
SELECT DISTINCT b1.reply_user, b2.avatar_link
FROM `dozhan_reply` b1, `dozhan_user` b2
WHERE `reply_article` = 69
AND b1.reply_user = b2.username 
solve, do not understand, grammar is not a problem?