在MySQL中处理日期？

Question

编辑：改变对不起，我尝试处理MySQL的DATETIME值， 这是我的MySQL查询的整个问题：

$result="SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m. m.dt 
FROM relationships r, notes m, user u 
WHERE m.user_id = r.leader 
AND r.leader = u.user_id 
AND r.listener ='".$_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 "; 

我尝试从该查询不是“$ lastmsg”年长找到行，而不是$ lastmsg本身，我想过使用少于但不等于操作符！我不知道这是愚蠢的！

查询的工作原理，但它的错误信息！

Answer 1

您只限制UNION下半部分的日期。试试这个：

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 

Answer 2

难道不应该着眼于日期查询片段是

AND dt > '".$lastmsg."' 

？