MySQL查询从WP_PostMeta行到列

Question

我正在尝试从wordpress表wp_postmeta进行查询 我需要下面图片中_form_id到_sub_id的数据。 我正在使用这个sql

SELECT meta_value,
MAX(CASE WHEN meta_key = '_field_14' THEN meta_value END) as a1,
MAX(CASE WHEN meta_key = '_field_15' THEN meta_value END) as a2,
MAX(CASE WHEN meta_key = '_field_17' THEN meta_value END) as a3,
MAX(CASE WHEN meta_key = '_field_18' THEN meta_value END) as a4
FROM wp_postmeta
Group by post_id

但是a1到a4上的NULL数据仍会显示在结果上。 我的SQL Fiddel 请指教，谢谢

预期结果

Answer 1

您需要选择post_id，group by中不存在meta_value，因此您将从每个帖子中获得随机值

此外，只有帖子54,56,57具有这些字段，因此其余帖子将获得NULL值。

SELECT post_id,
                MAX(CASE WHEN meta_key = '_field_14' THEN meta_value  END) as a1,
                MAX(CASE WHEN meta_key = '_field_15' THEN meta_value  END) as a2,
                MAX(CASE WHEN meta_key = '_field_17' THEN meta_value  END) as a3,
                MAX(CASE WHEN meta_key = '_field_18' THEN meta_value  END) as a4
                FROM wp_postmeta
                Group by post_id

编辑：

根据结果，您只需要来自所有具有值的帖子的元值，您可以使用子查询和合并来获得您想要的内容

SELECT * FROM
(
SELECT 
       MAX(CASE WHEN meta_key = '_field_14' THEN meta_value END) as a1,
       MAX(CASE WHEN meta_key = '_field_15' THEN meta_value END) as a2,
       MAX(CASE WHEN meta_key = '_field_17' THEN meta_value END) as a3,
       MAX(CASE WHEN meta_key = '_field_18' THEN meta_value END) as a4
FROM wp_postmeta
Group by post_id
)T
where coalesce(a1,a2,a3,a4) is not null