SQL Wordpress 查询 - 内部与外部联接

Question

我正在尝试获取 wp_postmeta 表具有 (meta_key='propdetails' AND meta_value LIKE '%Vacant Unrented Ready%') 或 (meta_key='featured' AND meta_value='on') 的所有帖子。

我现有的查询（如下）正在工作，除非 meta_key 'featured' 行缺失。然后，该帖子不会被退回。

同样，为了匹配行，我还需要检索我想要得到的meta_value，其中meta_key='martygeocoderlatlng'。但是，如果缺少该 meta_key，则根本不会返回整个帖子。

所以我需要使用我现有的查询并将meta_key='featured' 或meta_key='martygeocoderlatlng' 设为可选，因此如果它们不存在，我仍然可以进行其他比较并获取我需要的数据。

（我认为这可以通过某种方式使用 OUTER JOIN 来完成，但我无法完全理清语法。）

这是我现有的查询，它只返回 wp_postmeta 表中存在 meta_key='featured' 和 meta_key='martygeocoderlatlng' 的行（当然，满足 WHERE 子句中的其他条件）：

SELECT 
    p.*,
    pm.*,
    pm_featured.meta_value AS featured,
    pm_latlng.meta_value AS latlng

FROM 
    wp_posts p
    JOIN wp_postmeta pm
      ON pm.post_id = p.ID
    JOIN wp_postmeta pm_propdetails
      ON (pm_propdetails.post_id = p.ID AND pm_propdetails.meta_key = 'propdetails')
    JOIN wp_postmeta pm_featured
      ON (pm_featured.post_id = p.ID AND pm_featured.meta_key = 'featured-property')
    JOIN wp_postmeta pm_latlng
      ON (pm_latlng.post_id = p.ID AND pm_latlng.meta_key = 'martygeocoderlatlng')

    JOIN wp_term_relationships tr
      ON tr.object_id = p.ID
    JOIN wp_term_relationships tr_taxrel
      ON (tr_taxrel.object_id = p.ID AND tr_taxrel.term_taxonomy_id = 12)

WHERE
    (pm_propdetails.meta_value LIKE '%Vacant Unrented Ready%'
        OR
     pm_featured.meta_value = 'on')

    AND p.post_type = 'property'
    AND p.post_status = 'publish'

GROUP BY p.ID
ORDER BY p.post_date DESC

Answer 1

这是一个非常激烈的查询。如果不更好地了解您的表结构，很难确切地知道如何有效地执行此操作（似乎可以组合其中的一些 JOINS）。

这里只是通过编辑您的原始查询来实现的：

SELECT 
    p.*,
    pm.*,
    pm_featured.meta_value AS featured,
    pm_latlng.meta_value AS latlng

FROM 
    wp_posts p
    JOIN wp_postmeta pm
      ON pm.post_id = p.ID
    JOIN wp_postmeta pm_propdetails
      ON (pm_propdetails.post_id = p.ID AND pm_propdetails.meta_key = 'propdetails')
    LEFT JOIN wp_postmeta pm_featured
      ON (pm_featured.post_id = p.ID AND pm_featured.meta_key = 'featured-property')
    LEFT JOIN wp_postmeta pm_latlng
      ON (pm_latlng.post_id = p.ID AND pm_latlng.meta_key = 'martygeocoderlatlng')

    JOIN wp_term_relationships tr
      ON tr.object_id = p.ID
    JOIN wp_term_relationships tr_taxrel
      ON (tr_taxrel.object_id = p.ID AND tr_taxrel.term_taxonomy_id = 12)

WHERE
    (pm_propdetails.meta_value LIKE '%Vacant Unrented Ready%'
        OR
     (pm_featured.meta_value = 'on' OR pm_feature.meta_value IS NULL))

    AND p.post_type = 'property'
    AND p.post_status = 'publish'

GROUP BY p.ID
ORDER BY p.post_date DESC

它只是使用 LEFT JOIN 来尝试返回可能缺少 meta_key 的帖子，然后修改 WHERE 部分以尝试说明 pm_featured.meta_value 是否为 NULL。

如果您提供更多信息，可以尝试其他版本。

编辑： 根据您的问题，这也可能有效。不过真的只是在黑暗中拍摄了一个巨大的镜头=）

SELECT T2.*, T1.featured, T1.latlng FROM
(
    SELECT post_id, SUM(IF((meta_key='propdetails' AND meta_value LIKE '%Vacant Unrented Ready%') OR ((meta_key='featured' AND meta_value='on')),1,0)) AS Keeper
    , MAX(IF(meta_key = 'featured-property',meta_value,NULL)) AS featured
    , MAX(IF(meta_key = 'martygeocoderlatlng',meta_value,NULL)) AS latlng
    FROM wp_postmeta 
    GROUP BY post_id
    HAVING Keeper>0
) AS T1
JOIN
wp_posts AS T2
ON T1.post_id=T2.ID
AND T2.post_type = 'property'
AND T2.post_status = 'publish'
JOIN
wp_term_relationships AS T3
ON T2.ID=T3.object_id AND T3.term_taxonomy_id = 12
GROUP BY T2.ID
ORDER BY T2.post_date DESC

由于第二个查询最终起作用（有点令人惊讶，我做了很多假设；）这个应该稍微快一些并且更容易理解...... （注意：特别是如果您在 wp_postmeta 表中的 (meta_key,meta_value) 上有一个复合索引。）

SELECT T2.*, T1.featured, T1.latlng FROM
(
    SELECT postmetas_info.post_id
    , MAX(IF(meta_key = 'featured-property',meta_value,NULL)) AS featured
    , MAX(IF(meta_key = 'martygeocoderlatlng',meta_value,NULL)) AS latlng
    FROM 
    (
        SELECT DISTINCT post_id FROM wp_postmeta WHERE (meta_key='propdetails' AND meta_value LIKE '%Vacant Unrented Ready%') OR (meta_key='featured' AND meta_value='on')
    ) AS postmetas_applicable
    JOIN
    wp_postmeta AS postmetas_info
    ON postmetas_applicable.post_id=postmetas_info.post_id
    GROUP BY postmetas_info.post_id
) AS T1
JOIN
wp_posts AS T2
ON T1.post_id=T2.ID
AND T2.post_type = 'property'
AND T2.post_status = 'publish'
JOIN
wp_term_relationships AS T3
ON T2.ID=T3.object_id AND T3.term_taxonomy_id = 12
GROUP BY T2.ID
ORDER BY T2.post_date DESC

上一个查询中的 SUM(IF()) 很有趣，但可能没有它应有的性能，因为它会计算表中的每一行。上面的查询首先减少了 post_id，然后仅根据符合条件的 post_id 抓取相应的数据。