Joining/summing WordPress 数据库查询中的自定义字段

Question

尽管用谷歌搜索了 2 小时并尝试了各种 JOINS、UNIONS 和 ALIASES 等等，我仍然无法在一个 table 中检索 wp_postmeta 中两个子查询的结果 table 来自 WordPress 数据库（我什至不关心这里的 wp_posts，我感兴趣的所有数据都在 postmeta 中）。

我在数据库中有自定义字段（使用 ACF 插件管理），如下所示，一个键用于区域，另一个键用于数值。

|   ID   |   meta_key           |   meta_value   |
|   1    |   group_name         |   Japan        |
|   1    |   facility_index     |   0.83         |
|   2    |   group_name         |   USA          |
|   2    |   facility_index     |   4.51         |

我需要一个 returns 以下的查询，以便我可以按区域计算聚合（例如，所有设施的 facility_index 的总和，按 country/region，即按group_name):

|   ID   |   group_name  |   facility_index   |
|   1    |   Japan       |   0.83             |
|   2    |   USA         |   4.51             |

此查询两次列出 group_name，而不是在第 3 列中列出 facility_index：

SELECT post_id, meta_value, result2.meta_value FROM
(
(
SELECT post_id, meta_value
FROM wp_postmeta
WHERE meta_key = "group_name"
)
UNION
(
SELECT post_id, meta_value
FROM wp_postmeta
WHERE meta_key = "facility_index"
)
) AS result2
GROUP BY post_id

编辑以显示完全符合我要求的最终查询，感谢下面接受的答案：

SELECT
  meta1.meta_value AS group_name,
  meta2.meta_value AS facility_index,
  SUM(meta2.meta_value) AS 'fac_index_geo' 
FROM wp_posts post
  LEFT JOIN wp_postmeta meta1 ON meta1.post_id = post.ID AND meta1.meta_key = 'group_name'
  LEFT JOIN wp_postmeta meta2 ON meta2.post_id = post.ID AND meta2.meta_key = 'facility_index'
WHERE
  post.post_type = 'facility'
  GROUP BY group_name

Answer 1

据我了解，您正在寻找自定义 SQL 查询 - 即您不想使用 WP_Query 对象。

为此，我将使用一些 JOINS 而不是子查询。此外，我鼓励您查询 post_type，否则您可能会从 autosaves/revisions 或类似的错误结果中获取数据。

/*
INNER JOIN
This query will only return posts that contain all meta values
i.e. all 'post' items with group_name AND facility_index
*/
$sql = "
SELECT
  post.ID,
  meta1.meta_value AS group_name,
  meta2.meta_value AS facility_index
FROM {$wpdb->posts} post
  INNER JOIN {$wpdb->postmeta} meta1 ON meta1.post_id = post.ID AND meta1.meta_key = 'group_name'
  INNER JOIN {$wpdb->postmeta} meta2 ON meta2.post_id = post.ID AND meta2.meta_key = 'facility_index'
WHERE
  post.post_type = 'post'
";

$data = $wpdb->get_results( $sql );

只需确保更新 post_type 条件以匹配您所需的 post 类型。

或者，如果您还想获得缺少元值的 post，您可以使用此查询

/* 
LEFT JOIN
This query will return all posts even if they have missing meta values
i.e. if group_name or facility_index is empty, then NULL is returned in the column
*/
$sql = "
SELECT
  post.ID,
  meta1.meta_value AS group_name,
  meta2.meta_value AS facility_index
FROM {$wpdb->posts} post
  LEFT JOIN {$wpdb->postmeta} meta1 ON meta1.post_id = post.ID AND meta1.meta_key = 'group_name'
  LEFT JOIN {$wpdb->postmeta} meta2 ON meta2.post_id = post.ID AND meta2.meta_key = 'facility_index'
WHERE
  post.post_type = 'post'
";

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