1.UNION查詢沒問題

SELECT `id`,`username`,`mobile`,`time`,id AS leader 
FROM `grouporder_leader` 
WHERE `courseid` = 21 AND `merchid` = 23 AND `status` = 1 
UNION ALL 
SELECT leadorderid,username,mobile,time,null 
FROM `grouporder_partner`
WHERE courseid=21 and status=1 and merchid=23

2.排序就出問題了

SELECT `id`,`username`,`mobile`,`time`,id AS leader 
FROM `grouporder_leader`
WHERE `courseid` = 21 AND `merchid` = 23 AND `status` = 1 
ORDER BY time DESC 
UNION ALL 
SELECT leadorderid,username,mobile,time,null 
FROM `grouporder_partner`
WHERE courseid=21 and status=1 and merchid=23 
ORDER BY time DESC
 

使用類似於建立臨時表的方法儲存查詢結果，然後對臨時表進行查詢排序。

SELECT id,username,mobile,time,leader 
FROM (SELECT `id`,`username`,`mobile`,`time`,id AS leader 
	FROM `grouporder_leader` WHERE `courseid` = 21 AND `merchid` = 23 AND `status` = 1 
	UNION ALL 
	SELECT leadorderid,username,mobile,time,null 
	FROM `grouporder_partner` WHERE courseid=21 and status=1 and merchid=23
) 
ORDER BY time DESC
 

不知道為什麼第3步中查詢依舊沒有，然後對UNION查詢的結果起個別名，然後再查詢排序就沒問題了。

SELECT a.id,a.username,a.mobile,a.time,a.leader 
FROM (SELECT `id`,`username`,`mobile`,`time`,id AS leader 
	FROM `grouporder_leader` WHERE `courseid` = 21 AND `merchid` = 23 AND `status` = 1 
	UNION ALL 
	SELECT leadorderid,username,mobile,time,null 
	FROM `grouporder_partner` WHERE courseid=21 and status=1 and merchid=23
) AS a 
ORDER BY time DESC
 

查出來就好說了,再進行去重或者其他操作,也沒問題.

SELECT DISTINCT a.id,a.username,a.mobile,FROM_UNIXTIME(a.time,'%Y/%m/%d') as _time,a.leader 
FROM (SELECT `id`,`username`,`mobile`,`time`,id AS leader 
	FROM `grouporder_leader` WHERE `courseid` = 21 AND `merchid` = 23 AND `status` = 1 
	UNION ALL 
	SELECT leadorderid,username,mobile,time,null 
	FROM `grouporder_partner` WHERE courseid=21 and status=1 and merchid=23
) AS a 
ORDER BY time DESC