Question

我正在尝试运行查询来更新WordPress wp_postmeta表中自定义字段的值。数据如下所示：

meta_id     post_id     meta_key          meta_value
-------     -------     -------           ----------
1           1           start_date        2011-12-30
2           1           start_time        21:00
3           363         start_date        2011-12-29
4           363         start_time        21:00
5           363         _start_timestamp  2011-12-29 21:00

我想查询添加meta_key值为_start_timestamp的记录，该记录结合了给定post_id的start_date和start_time值，但是仅在尚未设置_start_timestamp的情况下。

在进入INSERT查询之前，我试图获得一个可以显示我想要的东西的SELECT查询。我设法创建一个SELECT查询，返回已定义_start_timestamp的帖子ID，但无法弄清楚如何获取没有定义的帖子ID。

这就是我所拥有的：

SELECT 
a.post_id, 
CONCAT(a.meta_value, ' ', b.meta_value), 
c.meta_value
FROM 
wp_postmeta a
INNER JOIN wp_postmeta b ON a.post_id=b.post_id
INNER JOIN wp_postmeta c ON a.post_id=c.post_id
WHERE 
a.meta_key = 'start_date' 
AND b.meta_key = 'start_time' 
AND c.meta_key='_start_eventtimestamp'

返回

post_id     CONCAT(a.meta_value, ' ', b.meta_value)     meta_value
363         2011-12-29 21:00                                2011-12-29 21:00

如果指定_start_timestamp的{{1}}列中不存在meta_key，我该如何指定获取结果？在这种情况下，它应该只返回post_id 1。

Answer 1

尝试：

SELECT 
a.post_id, 
CONCAT(a.meta_value, ' ', b.meta_value), 
c.meta_value
FROM 
wp_postmeta a
INNER JOIN wp_postmeta b ON a.post_id=b.post_id
LEFT JOIN wp_postmeta c ON a.post_id=c.post_id AND 
                           c.meta_key='_start_eventtimestamp'
WHERE 
a.meta_key = 'start_date' 
AND b.meta_key = 'start_time' 
AND c.post_id is null

编辑：另一种方法：

SELECT post_id,
       '_start_timestamp' as meta_key,
       concat(max(case meta_key when 'start_date' then meta_value end), ' ',
              max(case meta_key when 'start_time' then meta_value end) 
             ) as meta_value
from wp_postmeta
group by post_id
having max(case meta_key when 'start_date' then meta_value end) is not null and
       max(case meta_key when 'start_time' then meta_value end) is not null and
       max(case meta_key when '_start_timestamp' then meta_value end) is null

通过缺少值来过滤结果

1 个答案: