将两个SQL语句合并为一个语句

Question

我已经研究了将多个sql语句组合为一个，但无法使其工作。

我基本上有两个陈述，我想合并为一个将被查询的陈述。

这里有两种说法：

$sql="SELECT DISTINCT u.".($config->realnames ? "name" : "username")." AS displayname, u.id 
FROM (#__users AS u INNER JOIN #__uddeim AS um ON u.id=um.fromid) 
WHERE um.toid=".(int)$myself." AND um.totrash=0 AND `um`.`delayed`=0".$filter. 


$sql2="SELECT DISTINCT u.".($config->realnames ? "name" : "username")." AS displayname, u.id 
FROM (#__users AS u INNER JOIN #__uddeim AS um ON u.id=um.toid) 
WHERE um.fromid=".(int)$myself." AND um.totrashoutbox=0".$filter." AND um.systemflag=0" 

这里是我用两个别名“U”他们结合的尝试，和“o”：

$filter=""; 
if ($filter_user) $filter = " AND um.fromid=".(int)$filter_user; 
if ($filter_user==-1) $filter = " AND um.fromid=0"; 
if ($filter_unread) $filter .= " AND um.toread=0"; 
if ($filter_flagged) $filter .= " AND um.flagged<>0"; 

$sql= "SELECT DISTINCT u.".($config->realnames ? "name" : "username")." AS displayname, u.id, o.".($config->realnames ? "name" : "username")." AS displayname, o.id 
FROM (#__users AS u INNER JOIN #__uddeim AS um ON u.id=um.fromid) INNER JOIN #__uddeim AS om ON o.id=om.toid 
WHERE um.toid=".(int)$myself." AND um.totrash=0 AND `um`.`delayed`=0".$filter. " AND om.fromid=".(int)$myself." AND om.totrashoutbox=0".$filter." AND om.systemflag=0"; 

但这快到了没有结果，前两个陈述中，单独工作正常。

任何帮助表示赞赏。

Answer 1

尝试这个办法：在查询一个应该做到底

$sql=" 
SELECT 
    DISTINCT u.".($config->realnames ? "name" : "username")." AS displayname, 
    u.id 
FROM 
    (#__users AS u 
INNER JOIN 
    #__uddeim AS um 
ON 
    u.id=um.fromid) 
WHERE 
    um.toid=".(int)$myself." 
AND 
    um.totrash=0 
AND 
    `um`.`delayed`=0".$filter." 
UNION ALL 
SELECT 
    DISTINCT u.".($config->realnames ? "name" : "username")." AS displayname, 
    u.id 
FROM 
    (#__users AS u 
INNER JOIN 
    #__uddeim AS um 
ON 
    u.id=um.toid) 
WHERE 
    um.fromid=".(int)$myself." 
AND 
    um.totrashoutbox=0".$filter." 
AND um.systemflag=0"