Question

我有一个包含以下表格的WordPress数据库

帖子

+--------------+
| Field        |
+--------------+
| ID           |
| post_author  |
| post_title   | 
| post_type    | 
+--------------+

postmeta

+--------------+
| Field        |
+--------------+
| meta_id      |
| post_id      |
| meta_key     |
| meta_value   |
+--------------+

并拥有meta_key值latitude和longitude

的记录

如何编写SQL以显示latitude和longitude作为结果列名称？

+--------------+
| Field        |
+--------------+
| ID           |
| post_author  |
| post_title   |
| latitude     |
| longitude    | 
+--------------+

以下查询是我的出发点

SELECT ID, post_title, meta_key, meta_value FROM `wp_posts` 
LEFT JOIN `wp_postmeta` on ID=post_id 
WHERE post_type='place' AND (meta_key='latitude' OR meta_key='longitude') 
ORDER BY ID ASC

Answer 1

听起来您想要PIVOT latitude和longitude值PIVOT。不幸的是，MySQL没有CASE函数，但您可以使用带有SELECT p.ID, p.post_title, p.post_author, max(case when pm.meta_key='latitude' then pm.meta_value end) latitude, max(case when pm.meta_key='longitude' then pm.meta_value end) longitude FROM `wp_posts` p LEFT JOIN `wp_postmeta` pm on p.ID=pm.post_id WHERE p.post_type='place' AND (pm.meta_key='latitude' OR pm.meta_key='longitude') GROUP BY p.ID, p.post_title, p.post_author ORDER BY p.ID ASC语句的聚合函数来复制它：

{{1}}

请参阅SQL Fiddle with Demo

Answer 2

您可以使用以下内容：

SELECT
  wp_posts.ID,
  wp_posts.post_title,
  wp_post_1.meta_value as latitude,
  wp_post_2.meta_value as longitude
FROM
  wp_posts
  LEFT JOIN wp_postmeta wp_post_1
  ON wp_posts.ID=wp_post_1.post_id and wp_post_1.meta_key = 'latitude'
  LEFT JOIN wp_postmeta wp_post_2
  ON wp_posts.ID=wp_post_2.post_id and wp_post_2.meta_key = 'longitude'
WHERE post_type='place'
ORDER BY ID ASC

选择连接表的列值作为结果列名称

2 个答案: