在mysql中处理日期？

Question

编辑：更改整个问题抱歉，我试图处理mysql DATETIME值，这是我的mysql查询：

$result="SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m. m.dt
FROM relationships r, notes m, user u
WHERE m.user_id = r.leader
AND r.leader = u.user_id
AND r.listener ='".$_SESSION['user_id']."'
UNION
SELECT username, picture, id, user_note, reply_id, reply_name, dt
FROM user u, notes b
WHERE u.user_id = b.user_id
AND b.user_id = '".$_SESSION['user_id']."'
AND dt < '".$lastmsg."'
ORDER BY dt DESC
LIMIT 10 ";

我试图从此查询中查找早于'$ lastmsg'而不是$ lastmsg本身的行，我考虑使用小于但不等于运算符！ 林不知道这是愚蠢的！

PS查询工作，但它检索错误的信息！

Answer 1

查看日期的查询片段不应该是

AND dt > '".$lastmsg."'

？

Answer 2

您仅将日期限制在UNION的后半部分。 尝试以下方法：

SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m.dt
FROM relationships r, notes m, user u
WHERE m.user_id = r.leader
AND r.leader = u.user_id
AND r.listener ='".$_SESSION['user_id']."'
AND m.dt < '".$lastmsg."'
UNION 
SELECT username, picture, id, user_note, reply_id, reply_name, dt
FROM user u, notes b
WHERE u.user_id = b.user_id
AND b.user_id = '".$_SESSION['user_id']."'
AND dt < '".$lastmsg."'
ORDER BY dt DESC
LIMIT 10