对此查询引入联接，可能吗？

Question

我试图向此查询引入联接：

SELECT `n`.*, round((`n`.`rgt` - `n`.`lft` - 1) / 2, 0) AS childs, 
count(*) - 1 + (`n`.`lft` > 1) + 1 AS level, 
((min(`p`.`rgt`) - `n`.`rgt` - (`n`.`lft` > 1)) / 2) > 0 AS lower, 
(((`n`.`lft` - max(`p`.`lft`) > 1))) AS upper 
FROM `exp_node_tree_6` `n`, `exp_node_tree_6` `p`, `exp_node_tree_6`
WHERE `n`.`lft` 
BETWEEN `p`.`lft` 
AND `p`.`rgt` 
AND ( `p`.`node_id` != `n`.`node_id` OR `n`.`lft` = 1 )
GROUP BY `n`.`node_id` 
ORDER BY `n`.`lft`

添加

LEFT JOIN `exp_channel_titles`
ON (`n`.`entry_id`=`exp_channel_titles`.`entry_id`)

通过在 FROM 语句之后

...但是当我引入它时，它失败并显示“'on 子句'中的未知列'n.entry_id'”

是否可以添加对此查询的联接？

有谁可以帮忙吗，谢谢！

Answer 1

我想您的问题来自于您在表列表末尾添加了 join 子句。尝试

SELECT `n`.*, round((`n`.`rgt` - `n`.`lft` - 1) / 2, 0) AS childs, 
count(*) - 1 + (`n`.`lft` > 1) + 1 AS level, 
((min(`p`.`rgt`) - `n`.`rgt` - (`n`.`lft` > 1)) / 2) > 0 AS lower, 
(((`n`.`lft` - max(`p`.`lft`) > 1))) AS upper 
FROM `exp_node_tree_6` `n`
     LEFT JOIN `exp_channel_titles`
     ON (`n`.`entry_id`=`exp_channel_titles`.`entry_id`),

     `exp_node_tree_6` `p`,
     `exp_node_tree_6`
WHERE `n`.`lft` 
BETWEEN `p`.`lft` 
AND `p`.`rgt` 
AND ( `p`.`node_id` != `n`.`node_id` OR `n`.`lft` = 1 )
GROUP BY `n`.`node_id` 
ORDER BY `n`.`lft`

您只能在 ON 子句中引用属于 JOIN 流中已存在的表的字段。

我希望这对你有帮助
杰罗姆·瓦格纳