我们有时候需要在当前分类下自动获取所有文章的所有标签，来进行自动标签筛选。那么要获取当前分类下所有文章的所有标签聚合，可以使用以下的MySQL查询语句：
SELECT DISTINCT wp_terms.term_id, wp_terms.name, wp_terms.slug FROM wp_terms INNER JOIN wp_term_taxonomy ON wp_terms.term_id = wp_term_taxonomy.term_id INNER JOIN wp_term_relationships ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id INNER JOIN wp_posts ON wp_term_relationships.object_id = wp_posts.ID WHERE wp_term_taxonomy.taxonomy = 'post_tag' AND wp_term_taxonomy.term_id IN ( SELECT term_id FROM wp_term_taxonomy WHERE taxonomy = 'category' AND term_id = [当前分类ID] ) AND wp_posts.post_status = 'publish' 其中，[当前分类ID]需要替换为实际的分类ID。
这个查询语句会返回当前分类下所有文章的所有标签的聚合结果，包括每个标签的ID、名称和slug。
如果你想在WordPress中使用这个查询语句，可以使用$wpdb对象来执行查询，示例代码如下：
global $wpdb; $tags = $wpdb->get_results(" SELECT DISTINCT wp_terms.term_id, wp_terms.name, wp_terms.slug FROM {$wpdb->terms} AS wp_terms INNER JOIN {$wpdb->term_taxonomy} AS wp_term_taxonomy ON wp_terms.term_id = wp_term_taxonomy.term_id INNER JOIN {$wpdb->term_relationships} AS wp_term_relationships ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id INNER JOIN {$wpdb->posts} AS wp_posts ON wp_term_relationships.object_id = wp_posts.ID WHERE wp_term_taxonomy.taxonomy = 'post_tag' AND wp_term_taxonomy.term_id IN ( SELECT term_id FROM {$wpdb->term_taxonomy} WHERE taxonomy = 'category' AND term_id = [当前分类ID] ) AND wp_posts.post_status = 'publish' "); 这个代码会返回一个包含所有标签聚合结果的数组，每个元素是一个对象，包含term_id、name和slug三个属性。
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