工會選擇和ORDER BY與MySQL

Question

我想選擇使用工會從不同的表中的項目，通過他們的日期（最新的在前）

說我有以下各表

events 
eventsID | eventsTitle  | eventsTimestamp | eventsLocation 
1   event title   2012/08/23   1 
2   event title 2  2012/08/15   1 


posts 
postsID | postsSubject | postsTimestamp | postsCategory 
1   post title  2012/08/20   1 

於是下令輸出應該是

title   timestamp 
event Title  2012/08/23 
post title  2012/08/20 
event title 2  2012/08/15 

這裏就是我試圖做的，但我通過

得到的順序錯誤

SELECT posts.postsID, posts.postsSubject FROM posts where posts.postsCategory = 1 ORDER BY posts.postsTimestamp DESC 
UNION 
SELECT events.eventsID, events.eventsTitle FROM events where events.eventsLocation = 1 ORDER BY events.eventsTimestamp DESC 

Answer 1

你只需要一個ORDER BY條款，到了最後，經過2種聯合在一起選擇：

SELECT postsID   AS id, 
     postsSubject  AS title, 
     postsTimestamp AS timestamp 
FROM posts 
WHERE postsCategory = 1 

UNION 

SELECT eventsID, 
     eventsTitle, 
     eventsTimestamp 
FROM events 
WHERE eventsLocation = 1 

ORDER BY timestamp DESC ; 

Answer 2

試試這個，

SELECT Title, `TimeStamp` 
(
    SELECT posts.postsID as ID, 
      posts.postsSubject as Title, 
      eventsTimestamp as `TimeStamp` 
    FROM posts 
    where posts.postsCategory = 1 
    UNION 
    SELECT events.eventsID as ID, 
      events.eventsTitle as Title, 
      postsTimestamp as `TimeStamp` 
    FROM events 
    where events.eventsLocation = 1 
) x 
ORDER BY `TimeStamp` DESC 

Answer 3

由於UNION Syntax中提到：

要使用ORDER BY或LIMIT子句對整個進行排序或限制結果，將單個SELECT語句括起來，並在最後一個之後放置ORDER BY或LIMIT。下面的示例使用這兩種條款：

(SELECT a FROM t1 WHERE a=10 AND B=1) 
UNION 
(SELECT a FROM t2 WHERE a=11 AND B=2) 
ORDER BY a LIMIT 10;

因此：

(SELECT postsSubject AS title, postsTimestamp AS timestamp 
    FROM posts 
    WHERE postsCategory = 1) 

UNION ALL 

(SELECT eventsTitle, eventsTimestamp 
    FROM events 
    WHERE eventsLocation = 1) 

ORDER BY timestamp DESC 

看到它的sqlfiddle。