LEFT JOIN不起作用

Question

我有2個分類標準：city和street。

我需要爲我的一個插件獲得postmeta。

工作的代碼只有一個分類：

SELECT * 
FROM $wpdb->postmeta 
LEFT JOIN $wpdb->posts ON($wpdb->posts.ID = $wpdb->postmeta.post_id) 
LEFT JOIN $wpdb->term_relationships ON ($wpdb->postmeta.post_id = $wpdb->term_relationships.object_id) 
LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id) 
WHERE meta_key LIKE 'rwp_rating%' 
    AND ($wpdb->term_taxonomy.taxonomy = 'city' 
     AND $wpdb->term_taxonomy.term_id = '2') 

，但如果我追加

AND ($wpdb->term_taxonomy.taxonomy = 'street' AND $wpdb->term_taxonomy.term_id = '5') 

返回空的結果。

我也想這樣做：

SELECT * 
FROM $wpdb->postmeta 
LEFT JOIN $wpdb->posts ON ($wpdb->posts.ID = $wpdb->postmeta.post_id) 
LEFT JOIN $wpdb->term_relationships ON ($wpdb->postmeta.post_id = $wpdb->term_relationships.object_id) 
LEFT JOIN $wpdb->term_taxonomy AS t1 ON ($wpdb->term_relationships.term_taxonomy_id = t1.term_taxonomy_id) 
LEFT JOIN $wpdb->term_taxonomy AS t2 ON ($wpdb->term_relationships.term_taxonomy_id = t2.term_taxonomy_id) 
WHERE meta_key LIKE 'rwp_rating%' 
    AND (t1.taxonomy = 'city' 
     AND t1.term_id = '2') 
    AND (t2.taxonomy = 'street' 
     AND t2.term_id = '3331'); 

而且它不工作壓力太大。

請注意：我需要同時匹配，如：city = 2 AND street = 2
不是：city = 2 OR street = 2

Answer 1

你第一次嘗試將無法工作，因爲一個單一的分類記錄不能兼得城市和街道在裏面。

更新你的第二次嘗試這樣的：

SELECT * FROM $wpdb->postmeta 
LEFT JOIN $wpdb->posts ON ($wpdb->posts.ID = $wpdb->postmeta.post_id) 
LEFT JOIN $wpdb->term_relationships ON ($wpdb->postmeta.post_id = $wpdb->term_relationships.object_id) 
LEFT JOIN $wpdb->term_taxonomy as t1 ON ($wpdb->term_relationships.term_taxonomy_id = t1.term_taxonomy_id AND t1.taxonomy = 'city') 
LEFT JOIN $wpdb->term_taxonomy as t2 ON ($wpdb->term_relationships.term_taxonomy_id = t2.term_taxonomy_id AND t2.taxonomy = 'street') 
WHERE meta_key LIKE 'rwp_rating%' AND t1.term_id = '2' AND t2.term_id = '3331');