Question

我有两张桌子：

wp_posts

ID  post_title                      post_date
20  Título de tuit de ejemplo       2012-12-03 20:24:58
23  Título de teletipo de ejemplo   2012-12-04 13:56:33
25  Título de Clipping de ejemplo   2012-12-04 14:16:14
28  Título 4 diciembre 2012         2012-12-04 14:48:05
32  Título de noticia Actualidad    2012-12-04 17:35:57
78  Título de Destacado de ejemplo  2012-12-05 23:19:38
110 Título de Clipping radio        2012-12-09 15:57:28
112 Título de Clipping televisión   2012-12-09 15:59:31

wp_postmeta

meta_id  post_id  meta_key            meta_value
61       20       wpcf-custom-author  John Doe
134      28       wpcf-custom-author  John Smith
85       23       wpcf-custom-author     
111      25       wpcf-custom-author     
176      32       wpcf-custom-author  John Smith
614      110      wpcf-custom-author     
524      78       wpcf-custom-author     
627      112      wpcf-custom-author     
538      80       wpcf-custom-author     
48       20       wpcf-source    
132      28       wpcf-source         El País
83       23       wpcf-source         El País
109      25       wpcf-source         El País
174      32       wpcf-source         El País
612      110      wpcf-source         El Mundo

这是正确的，这些是wordpress表，但我的问题是关于mysql，我需要一个查询，它从wp_postmeta中检索属于相同wp_posts.ID的几个字段，这样我就可以获得同一行的所有信息。到目前为止，我已经提出：

SELECT DISTINCT posts.post_title AS title,
posts.post_date AS publish_date, 
(SELECT subpostmeta.meta_value FROM wp_postmeta AS subpostmeta WHERE subpostmeta.post_id = postmeta.post_id AND subpostmeta.meta_key =  'wpcf-lead-in') AS lead_in,
(SELECT subpostmeta.meta_value FROM wp_postmeta AS subpostmeta WHERE subpostmeta.post_id = postmeta.post_id AND subpostmeta.meta_key =  'wpcf-custom-body') AS custom_body,
(SELECT subpostmeta.meta_value FROM wp_postmeta AS subpostmeta WHERE subpostmeta.post_id = postmeta.post_id AND subpostmeta.meta_key =  'wpcf-custom-author') AS custom_author,
(SELECT subpostmeta.meta_value FROM wp_postmeta AS subpostmeta WHERE subpostmeta.post_id = postmeta.post_id AND subpostmeta.meta_key =  'wpcf-source') AS source
FROM wp_posts AS posts, wp_postmeta AS postmeta
WHERE posts.ID = postmeta.post_id
AND posts.post_status = 'publish'
AND posts.post_type = 'contenido'
AND posts.post_date < NOW()
ORDER BY posts.post_date DESC

据我所知，这是正常的，因为我得到了：

post_title                          post_date               lead_in                                                 custom_body                                             custom_author   source
Título de noticia de ejemplo        2013-02-04 15:10:25     En un lugar de la Mancha, de cuyo nombre no quiero...   En un lugar de la Mancha, de cuyo nombre no quiero...   Juan García     ABC
Título de Clipping televisión       2012-12-09 15:59:31                                                             Clipping TV: Your bones don't break, mine do. That...                   La Vanguardia
Título de Clipping radio            2012-12-09 15:57:28                                                             Clipping radio: Now that we know who you are, I kn...                   El Mundo
Título de Destacado de ejemplo      2012-12-05 23:19:38                                                             Really?! We'll go deliver this crate like professi...

但是我不确定这是否是获得我想要的最佳方法，我已经阅读了LEFT JOIN并在过去使用它但不确定我是否可以在这里使用它或者它的优点是什么。

欢迎任何反馈！

编辑：我最后使用LEFT JOIN，所以我不确定如何投票或关闭此主题。它比我在这里写的要复杂一点，无论如何，这是我最后的查询：

    SELECT DISTINCT posts.*,
        posts.post_date                  AS publish_date,
        tbl_lead_in.meta_value           AS lead_in,
        tbl_custom_author.meta_value     AS custom_author,
        tbl_source.meta_value            AS source,
        tbl_category_terms.slug          AS category_term_slug,
        tbl_category_terms.term_id   AS category_term_id
    FROM $wpdb->posts AS posts
        LEFT JOIN $wpdb->postmeta AS tbl_lead_in
               ON ( posts.ID = tbl_lead_in.post_id
                    AND tbl_lead_in.meta_key = 'wpcf-lead-in' )
        LEFT JOIN $wpdb->postmeta AS tbl_custom_body ON
                  ( posts.ID = tbl_custom_body.post_id
                    AND tbl_custom_body.meta_key = 'wpcf-custom-body' )
        LEFT JOIN $wpdb->postmeta AS tbl_custom_author
               ON ( posts.ID = tbl_custom_author.post_id
                    AND tbl_custom_author.meta_key = 'wpcf-custom-author' )
        LEFT JOIN $wpdb->postmeta AS tbl_source
               ON ( posts.ID = tbl_source.post_id
                    AND tbl_source.meta_key = 'wpcf-source' )
        LEFT JOIN $wpdb->term_relationships AS tbl_category_rel
               ON (posts.ID = tbl_category_rel.object_id)
        RIGHT JOIN $wpdb->term_taxonomy AS tbl_category
               ON (tbl_category_rel.term_taxonomy_id = tbl_category.term_taxonomy_id
                    AND tbl_category.taxonomy = 'category')
        LEFT JOIN $wpdb->terms AS tbl_category_terms
               ON ( tbl_category_terms.term_id = tbl_category.term_id )
    WHERE posts.post_status = 'publish'

Answer 1

您正在尝试 pivot 将数据从行转换为列的数据。 MySQL没有透视功能，但您可以重写查询以使用带有CASE表达式的聚合函数，用于返回的每个列：

SELECT p.post_title,
  max(case when pm.meta_key = 'wpcf-lead-in' then pm.meta_value end) as lead_in,
  max(case when pm.meta_key = 'wpcf-custom-body' then pm.meta_value end) as custom_body,
  max(case when pm.meta_key = 'wpcf-custom-author' then pm.meta_value end) as custom_author,
  max(case when pm.meta_key = 'wpcf-source' then pm.meta_value end) as source
FROM wp_posts p
LEFT JOIN wp_postmeta pm
  ON p.id = pm.post_id
WHERE p.post_status = 'publish'
  AND p.post_type = 'contenido'
  AND p.post_date < NOW()
GROUP BY p.post_title
ORDER BY p.post_date DESC

MySQL如何从同一列中选择多个值，使它们出现在不同的列中？

1 个答案: