ORDER BY和LIMIT不工作時使用UNION

Question

這是我的查詢：

mysql_query("SELECT userid FROM messages WHERE userid<>'$myid' AND friendid='$myid' AND status=1 UNION SELECT friendid FROM messages WHERE userid='$myid' AND friendid<>'$myid' AND status=1"); 

我想添加分頁，所以我需要限制的朋友，我的消息的數量。但是每當我添加LIMIT時，它都會顯示錯誤。另外，我想先顯示最新消息ORDER BY time DESC但這不起作用。幫幫我 ？

Answer 1

附上一個子查詢和ORDER BY ... LIMIT...內部的查詢外一個：

SELECT * 
FROM 
(
    SELECT userid 
    FROM messages 
    WHERE userid <> '$myid' 
     AND friendid = '$myid' 
     AND status = 1 
    UNION 
    SELECT friendid 
    FROM messages 
    WHERE userid = '$myid' 
     AND friendid <> '$myid' 
     AND status = 1 
) AS sub 
ORDER BY ... 
LIMIT ...; 

Answer 2

嘗試也許

SELECT DISTINCT userid FROM...