试图构建复杂的嵌套连接

Question

我一直在试图找出加入这些查询的最佳方式，而且我很难过 - 我会在这方面寻求帮助！

查询1为我提供了我想要的行 - 查询2为我提供了另一个表中的条目，其中数据相对于查询1中的每一行

我似乎无法构建一个正确的语句来返回包含来自查询1的每一行中查询2的结果的行。注意：查询1中的“object_id AS id”=查询2中的“post_id”

查询1：

SELECT LEFT(post_content, 40) AS excerpt, id, post_title, guid FROM wp_posts 
   WHERE id IN 
    (SELECT object_id AS id FROM wp_term_relationships WHERE term_taxonomy_id = 74)

查询2：

SELECT post_id, 
  MAX(CASE WHEN meta_key = 'allowed' THEN meta_value END) allowed,
  MAX(CASE WHEN meta_key = 'amenities' THEN meta_value END) amenities,
  MAX(CASE WHEN meta_key = 'trail-type' THEN meta_value END) trailtype,
  MAX(CASE WHEN meta_key = 'weatherlat' THEN meta_value END) weatherlat,
  MAX(CASE WHEN meta_key = 'weatherlon' THEN meta_value END) weatherlon
from wp_postmeta WHERE post_id = ***id from Query 1***

查询1返回以下内容：

excerpt  |  id  |  post_title    |  guid
-----------------------------------------
data     |  1   |  example title |  link
data     |  2   |  example title |  link
data     |  3   |  example title |  link

查询2返回以下内容：

post_id  |  allowed  |  amenities  |  trailtype  |  weatherlat  |  weatherlon
------------------------------------------------------------------------------
    1    |  BOOL     |  a, b, c    |   1         |  53.12       |  -24.123

期望的结果是：

excerpt  |  id  |  post_title    |  guid  |  allowed  | amenities |  trailtype  |  weatherlat  |  weatherlon
-----------------------------------------
data     |  1   |  example title |  link  |  BOOL     |  a, b, c  |   1         |  53.12      |  -24.123
data     |  2   |  example title |  link  |  BOOL     |  d, e, f  |   2         |  23.67      |  56.42
data     |  3   |  example title |  link  |  BOOL     |  a, b, c  |   1         |  56.152     |  -50.123

Answer 1

这只是在语法上组合你的查询：

SELECT LEFT(a.post_content, 40) AS excerpt, a.id, a.post_title, a.guid, 
  MAX(CASE WHEN meta_key = 'allowed' THEN b.meta_value END) allowed,
  MAX(CASE WHEN meta_key = 'amenities' THEN b.meta_value END) amenities,
  MAX(CASE WHEN meta_key = 'trail-type' THEN b.meta_value END) trailtype,
  MAX(CASE WHEN meta_key = 'weatherlat' THEN b.meta_value END) weatherlat,
  MAX(CASE WHEN meta_key = 'weatherlon' THEN b.meta_value END) weatherlon
FROM wp_posts a
LEFT JOIN wp_postmeta b ON a.id = b.post_id
   WHERE a.id IN 
    (SELECT object_id AS id FROM wp_term_relationships WHERE term_taxonomy_id = 74)

Answer 2

这个where声明不会有效吗？

where post_id in (SELECT object_id AS id FROM wp_term_relationships WHERE term_taxonomy_id = 74)

在第一个查询中，id设置为这些object_id值之一。因此，外部查询不会添加任何内容（或取消任何内容）。

Answer 3

经过多次痛苦，痛苦，并且提出了3-4个未完整答案的问题（很多部分答案 - 感谢所有人），我已经构建了声明，以便返回的行完全是我想要的。

SELECT LEFT(a.post_content, 100) AS excerpt, a.id, a.post_title, a.guid, 
 MAX(CASE WHEN b.meta_key = 'allowed' THEN b.meta_value END) allowed,
 MAX(CASE WHEN b.meta_key = 'amenities' THEN b.meta_value END) amenities,
 MAX(CASE WHEN b.meta_key = 'trail-type' THEN b.meta_value END) trailtype,
 MAX(CASE WHEN b.meta_key = 'weatherlat' THEN b.meta_value END) weatherlat,
 MAX(CASE WHEN b.meta_key = 'weatherlon' THEN b.meta_value END) weatherlon
FROM wp_posts a
LEFT JOIN wp_postmeta b ON a.id = b.post_id
 WHERE a.id IN (SELECT object_id AS id FROM wp_term_relationships WHERE term_taxonomy_id = 74) group by b.post_id

结果是完美的！ 请参阅：