获取数据

Question

我得到了3个tabels：

• wp_posts
• wp_metadata
• 用户

当我从 “wp_posts” 我的查询我使用LEFT JOIN从“wp_metadata”获得的数据，但我怎么能得到从3 TABL值e“用户”？

例子： 我有我的wordpressblog一个职位。在那篇文章中，我有一些元字段 - 其中一个叫做“userid”。我的用户位于wordpress之外的表格中。如何从表格“用户”中获取用户名，其中后置元键“userid”等于“users” - 表行ID？

这里是我的SQL请求，因为它是现在：

SELECT ID, post_title, 
    post_excerpt, 
    post_content, 
    m.meta_value AS placeid, 
    i.meta_value AS photoid, 
    r.meta_value AS rating, 
    u.meta_value AS userid, 
    b.username 
FROM wp_posts p 
LEFT JOIN wp_postmeta m ON (m.post_id = p.ID) 
LEFT JOIN wp_postmeta i ON (i.post_id = p.ID) 
LEFT JOIN wp_postmeta r ON (r.post_id = p.ID) 
JOIN wp_postmeta u ON (u.post_id = p.ID) 
LEFT JOIN brugere b ON (b.id = userid) 
WHERE m.meta_key = 'placeid' 
AND i.meta_key = 'photoid' 
AND r.meta_key = 'rating' 
AND u.meta_key = 'userid' 
AND post_status = 'publish' 
ORDER BY ID DESC LIMIT 50; 

我想要一个查询，因为我使用一个“打印json_encode”查询。

Answer 1

SELECT p.* 
    , x.placeid 
    , x.photoid 
    , x.userid 
    , x.rating 
    , u.username 
    FROM wp_posts p 
    LEFT 
    JOIN 
    (SELECT post_id 
      , MAX(CASE WHEN meta_key = 'placeid' THEN meta_value END) placeid 
      , MAX(CASE WHEN meta_key = 'photoid' THEN meta_value END) photoid 
      , MAX(CASE WHEN meta_key = 'userid' THEN meta_value END) userid 
      , MAX(CASE WHEN meta_key = 'rating' THEN meta_value END) rating 
     FROM wp_postmeta 
     GROUP 
      BY post_id 
    ) x 
    ON x.post_id = p.id 
    LEFT 
    JOIN brugere u 
    ON u.id = x.userid; 

+----+--------------+--------------+----------------+-------------+-----------+---------+---------+--------+--------+----------+ 
| ID | post_content | post_title | post_excerpt | post_status | post_type | placeid | photoid | userid | rating | username | 
+----+--------------+--------------+----------------+-------------+-----------+---------+---------+--------+--------+----------+ 
| 1 | Content 1 | Post title 1 | Post ecxerpt 1 | publish  | post  | 101  | 102  | 2  | 4  | Bruger 2 | 
| 2 | Content 2 | Post title 2 | Post ecxerpt 2 | publish  | post  | 201  | 202  | 3  | 3  | Bruger 3 | 
| 3 | Content 3 | Post title 3 | Post ecxerpt 3 | publish  | post  | 301  | 302  | 3  | 2  | Bruger 3 | 
| 4 | Content 4 | Post title 4 | Post ecxerpt 4 | publish  | post  | NULL | NULL | NULL | NULL | NULL  | 
| 5 | Content 5 | Post title 5 | Post ecxerpt 5 | publish  | post  | NULL | NULL | NULL | NULL | NULL  | 
+----+--------------+--------------+----------------+-------------+-----------+---------+---------+--------+--------+----------+ 

http://sqlfiddle.com/#!2/f517a/10