Question

我在这里查了好几个帖子，找不到我问题的答案.... 我试图用多个表做一个mysql查询，然后离开加入最后一个表。它不喜欢左连接，当我包含它时没有给我任何结果。非常感谢任何帮助：）

（我正在使用Joomla）

query = "SELECT DISTINCT u.id as uid, CONCAT(u.first_name,' ',u.last_name) as name1,
 u.grad as   grad, u.opt_out as opt_out
FROM #__bl_teams as t, #__bl_regions as r, #__users as u 
LEFT JOIN #__bl_paid as pd ON pd.u_id = u.id

WHERE u.team_id = t.id AND u.team_id != '' AND u.s_id = $sid 
AND ((t.id = $tid)OR($tid=0)) AND (t.id IN ($teamsfull)) 
AND ( (t.id IN(".$tc_teams."))OR(".$tc_id." = 0)) 
AND ((r.id = ".$mid.")OR(".$mid." = 0)) 
AND ((r.s_id = ".$sid.")OR(".$mid." = 0)) 
AND ( (FIND_IN_SET(t.id,r.teams) )OR(".$mid." = 0) ) 
AND u.id NOT IN($paidrows) AND u.id NOT IN ($rsrows) GROUP BY u.id";
    $db->setQuery($query, $pageNav->limitstart, $pageNav->limit);
    $rows50 = $db->loadObjectList();

Answer 1

您正在混合旧式连接和新式连接。那是你的问题。在from语句中，表格别名无法以您期望的方式识别。埋在documentation中的是这个警告：

但是，逗号运算符的优先级小于INNER JOIN，CROSS JOIN，LEFT JOIN等等。如果你混合使用逗号连接当有连接条件时，其他连接类型，错误表格未知栏＆＃39; col_name＆＃39;在＆＃39; on条款＆＃39;可能导致。信息关于这个问题的处理将在本节后面给出。

简单规则：永远不要在from子句中使用逗号。

因此，使用显式连接重写您的查询，这将解决问题。

Answer 2

我不知道实际的表，但是这个查询太长并且会产生意外的结果。无论如何，Left也加入了其他表。

query = "SELECT DISTINCT u.id as uid, CONCAT(u.first_name,' ',u.last_name) as name1, 
u.grad as   grad, u.opt_out as opt_out

FROM #__users as u 

LEFT JOIN #__bl_paid as pd ON pd.u_id = u.id
LEFT JOIN #__bl_teams as t ON t.u_id = u.id
LEFT JOIN #__bl_regions as r ON r.u_id = u.id

WHERE u.team_id != '' 
AND u.s_id = $sid 
AND ((t.id = $tid)
OR($tid=0)) 
AND (t.id IN ($teamsfull)) 
AND ( (t.id IN(".$tc_teams."))
OR(".$tc_id." = 0)) 
AND ((r.id = ".$mid.")
OR(".$mid." = 0)) 
AND ((r.s_id = ".$sid.")
OR(".$mid." = 0)) 
AND ( (FIND_IN_SET(t.id,r.teams) )
OR(".$mid." = 0) ) 
AND u.id NOT IN($paidrows) 
AND u.id NOT IN ($rsrows) 
GROUP BY u.id";

Mysql多表离开加入最后一个表

2 个答案: