SQL 查询：将 Concat 子元素与父元素分组

Question

我正在尝试查询 WordPress 数据库以导出帖子列表及其内容。我一切正常，但不知道如何包含附加图像。我不知道如何在同一张表中将孩子与父母相关联。

父标识符位于 ID 列中，子标识符位于 post_parent 列中。我尝试连接的值位于名为 guid 的列中，其中包含图像的完整 URL（正是我需要的）。

wp_posts 表结构：

ID   post_parent   guid          post_type
1     0             http://...    attachment
2     1             http://...    attachment
3     1             http://...    attachment
4     1             http://...    attachment

这是我的查询：

SELECT DISTINCT
post_title
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-year' AND wap_postmeta.post_id = wap_posts.ID) AS "Year"
,(SELECT group_concat(wap_terms.name separator ', ') 
FROM wap_terms
INNER JOIN wap_term_taxonomy ON wap_terms.term_id = wap_term_taxonomy.term_id
INNER JOIN wap_term_relationships wpr ON wpr.term_taxonomy_id = wap_term_taxonomy.term_taxonomy_id
WHERE taxonomy= 'car-manufacturer' AND wap_posts.ID = wpr.object_id
) AS "Manufacturer"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-model' AND wap_postmeta.post_id = wap_posts.ID) AS "Model"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-trim' AND wap_postmeta.post_id = wap_posts.ID) AS "Trim"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-vin' AND wap_postmeta.post_id = wap_posts.ID) AS "VIN"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-odometer' AND wap_postmeta.post_id = wap_posts.ID) AS "Odometer"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-price' AND wap_postmeta.post_id = wap_posts.ID) AS "Price"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-extcolor' AND wap_postmeta.post_id = wap_posts.ID) AS "Exterior Color"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-intcolor' AND wap_postmeta.post_id = wap_posts.ID) AS "Interior Color"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-transmission' AND wap_postmeta.post_id = wap_posts.ID) AS "Transmission"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-engine' AND wap_postmeta.post_id = wap_posts.ID) AS "Engine"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-fuel' AND wap_postmeta.post_id = wap_posts.ID) AS "Fuel Type"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-drivetrain' AND wap_postmeta.post_id = wap_posts.ID) AS "Drivetrain"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-doors' AND wap_postmeta.post_id = wap_posts.ID) AS "car-doors"
,(SELECT meta_value FROM wap_postmeta WHERE wap_postmeta.meta_key = 'car-stockno' AND wap_postmeta.post_id = wap_posts.ID) AS "Stock #"
,(SELECT group_concat(wap_terms.name separator ', ') 
FROM wap_terms
INNER JOIN wap_term_taxonomy ON wap_terms.term_id = wap_term_taxonomy.term_id
INNER JOIN wap_term_relationships wpr ON wpr.term_taxonomy_id = wap_term_taxonomy.term_taxonomy_id
WHERE taxonomy= 'car-feature' AND wap_posts.ID = wpr.object_id
) AS "Features"
,(SELECT group_concat(wap_terms.name separator ', ') 
FROM wap_terms
INNER JOIN wap_term_taxonomy ON wap_terms.term_id = wap_term_taxonomy.term_id
INNER JOIN wap_term_relationships wpr ON wpr.term_taxonomy_id = wap_term_taxonomy.term_taxonomy_id
WHERE taxonomy= 'car-body-type' AND wap_posts.ID = wpr.object_id
) AS "Body Type"

-- MY PROBLEM STARTS HERE
,(SELECT group_concat(wap_posts.guid separator ', ') 
FROM wap_posts
WHERE wap_posts.post_type = 'attachment' AND wap_posts.post_parent = wap_posts.ID
) AS "Images"
-- MY PROBLEM ENDS HERE

FROM wap_posts
WHERE post_type = 'vehicle' AND post_status = 'publish'
ORDER BY
post_title

我意识到这会返回 NULL，因为附件的 post_parent 永远不会匹配它自己的 ID。我只是不知道如何告诉查询将 post_parent 值与父 ID 而不是它自己的 ID 匹配。

希望我已经发布了足够的信息，如果我应该包含任何其他数据，请告诉我。感谢阅读！

最好的问候， 周杰伦

Answer 1

您可以对同一张表执行left join 以产生所需的结果（假设并非每个帖子都有附件）

select     p.Id,group_concat(c.guid separator ', ') guids 
from wap_posts p
left join wap_posts c on (c.post_parent = p.id)

http://sqlfiddle.com/#!2/f7522/1/0