MySQL选择内部加入,仅限首先限制

Question

我需要从我的数据库中分页帖子,我写下一个查询:

SELECT posts.ID, posts.date, comments.name, comments.value 
FROM posts 
INNER JOIN comments 
    ON comments.ID = posts.ID 
INNER JOIN relations 
    ON relations.ID = posts.ID 
WHERE type_rel=1 AND status_post=1 AND 
LIMIT 0,10

问题出在LIMIT句子中,我只需要限制"posts"表.

评论表有很多行,如果我把限制放在"0,10","posts"表限制为10个帖子,但评论表也限制为10.

有人解决了我的问题吗？我在PHP查询中使用它.

抱歉我的英语不好,提前谢谢.

Answer 1

您可以使用子查询来限制结果集,然后加入:

SELECT 
  posts.ID, 
  posts.date, 
  comments.name, 
  comments.value 
FROM
  (SELECT * FROM posts WHERE status_post = 1 LIMIT 0,10) posts
LEFT JOIN 
  comments 
  ON comments.ID = posts.ID 
LEFT JOIN 
  relations 
  ON relations.ID = posts.ID AND relations.type_rel = 1

从注释中,索引文件中的查询是错误的,这是正确的:

SELECT 
  wp_posts.ID, 
  wp_posts.post_date, 
  wp_postmeta.meta_key, 
  wp_postmeta.meta_value 
FROM (SELECT * FROM wp_posts WHERE post_status="publish" AND post_type="post" LIMIT 0,2) wp_posts 
LEFT JOIN wp_postmeta 
  ON wp_postmeta.post_id = wp_posts.ID 
LEFT JOIN wp_term_relationships 
  ON wp_term_relationships.object_id = wp_posts.ID 
  AND wp_term_relationships.term_taxonomy_id=2

这里的示例结果,你可以看到你有两个帖子,id 1和5.

如果你想保留term_taxonomy_id = 2使用它的帖子:

SELECT 
  wp_posts.ID, 
  wp_posts.post_date, 
  wp_postmeta.meta_key, 
  wp_postmeta.meta_value 
FROM (
  SELECT * 
  FROM wp_posts 
  JOIN wp_term_relationships 
  ON wp_term_relationships.object_id = wp_posts.ID 
  AND wp_term_relationships.term_taxonomy_id = 2
  WHERE post_status="publish" AND post_type="post" LIMIT 0,2) wp_posts 
LEFT JOIN wp_postmeta ON wp_postmeta.post_id = wp_posts.ID

例如,post id为5和7,限制0,1仅返回5.